How to counter a team of multiple Torbjörns?

From my own experience, a Reinhardt or two is almost completely necessary. I would recommend throwing a Zenyatta in as well; despite being squishy, his orb of discorb is a huge help against Torbjorn, especially when he's pulled his Molten Core. The key to pushing past a Torbjorn defense is to kill him, that way, he cannot rebuild his turrets. A damage debuff is the key to quickly eliminating them.

As other answers have stated, snipers and the like (Pharah, Soldier: 76, etc) can all assist, and the absorb/reflect of D.VA and Genji is invaluable, but the debuff gained from Zenyatta's orb can make things all the more easy.

EDIT: I've often found that as soon as a wall of Torbs'n'Turrets is broken, the point is usually yours. The turrets are only truly dangerous as long as Torbjorn is still around. If you kill all the Torbs, they aren't likely to be able to setup a new defense on that point.

As several have said already, Genji, Pharah, Soldier 76, Zenyatta, and Reinhardt are all good picks against a team that has one or more Torbjörns. However you should also look at D.Va, Winston, Hanzo, Widowmaker, Junkrat, Tracer, Zarya, McCree, and Mei. All of these can help destroy turrets in the following ways.

• Genji can deflect turret damage back at the turrets to kill them.
• Pharah has long range damage with her rockets that do splash damage, so she can hurt the Torbjörn who is repairing the turret at the same time as damaging the turret. She can also knock the Torbjörn away from his turret with her E ability, and if someone is distracting the turrets, her ultimate can quickly clear out turret nests.
• Soldier 76 has good dps that is quite accurate at mid range, and a full clip or two into helix rockets will generally kill a turret.
• Zenyatta while being a support, does a lot of damage with his primary and alternate fire. If he is shielded, he can not only heal people who get low, but charge his alternate fire to help burst turrets down. He can also use transcendence to keep his team alive while pushing in to clear turrets.
• Reinhardt is pretty essential for killing turrets. While they may chip his shield down fairly quickly, he can provide protection for multiple members of his team who can all provide damage to destroy the turret.
• D.Va can use her mech to absorb a lot of damage from turrets, as well as completely negating a turrets damage if she uses defense matrix on it, allowing her to distract turrets for her teammates to kill. Also, when she gets her ultimate, she can easily clear a room or point where the turrets are setting up by boosting into an eject and letting the mech drop in on the turrets.
• Winston can thrown up a shield around a turret and completely prevent it from shooting his teammates outside. Also, his tesla can hit multiple targets which can help clear multiple turrets at a time. It may be a good idea to run multiple Winstons to counter multiple Torbjörns.
• Hanzo and Widowmaker can shoot down turrets for long range. Without getting hit by the turret. Hanzo has the added benefit of being able to arc arrows so he can hide at a slightly lower elevation and still hit the turrets.
• Junkrat can get his primary fire into hard to reach rooms to clear out turrets inside by bouncing them off walls. He can also arc his shots over walls to clear out turrets behind a wall. His ultimate can also quickly kill Torbjörns and their turrets if it isn't destroyed.
• Not as obvious, but Tracer can dart around a wall and get damage down on a Torbjörn or his turret and recall to safety. Doing this can eventually wear them down, and with ultimate up you can drop that on a Torbjörn to instantly kill him.
• Zarya can put up a barrier on whoever is being targeted by the turret and gain free charge while providing protection for his teammate. She can then used her super charged weapon to quickly damage turrets and destroy them.
• McCree, if he can find a good flank on the turret, can actually flash bang the turret so he can flash bang into fan the hammer for some good damage on the turret. He can kill the turret with this combo if he lands all of his fan the hammer shots.
• Mei is also a great counter to turrets, as she can wall them off to prevent LOS so that the turret cannot fire on her team. She can also freeze turrets with her primary fire or her ultimate.

Note: You should always have a healer to heal anyone who is taking damage while taking out the turret. Mercy can also damage boost people who are safe from the turret damage in order to more quickly kill it, and Lúcio's sound barrier can help negate most of the damage and give people enough health to kill the turrets. Sound barrier and resurrection can also help counter Molten Core.

I'd say something you are comfortable doing medium to long range damage with

Hanzo, Pharah, Widowmaker, Soldier 76, Zenyatta come to mind

If the turrets are 'Level 2', they have 300 health, so ideally you want to be able to do those 300 points of damage while receiving as little damage as possible.

A Reinhardt + 1 or more Soldier 76's would be a good combination. Soldier 76's shots + his rockets (right-click) can take out a Torbjorn turret in a few seconds.

Without a Reinhardt assisting, maybe Pharah would be a good choice, but I would suggest trying to corner-peak the turrets in this case. It should take 2-3 rockets to kill a turret, but if you are flying as Pharah, you could take a significant amount of damage or die. So again, without Reinhardt assisting, this is why I'd suggest corner-peaking to take the shots.

I could also suggest Junkrat. If you know the location of some of the turrets, you can usually find a spot you can hit them without actually seeing the turret. That is, you can launch Junkrat's grenades over a building, bounce them off a wall etc. to hit the turret without exposing yourself.

So I guess there are lots of options, but in general the idea seems to be you want to deal as much damage in as small an amount of time as possible, while reducing your exposure to the turre

I do love this strategy!

Generally the best counter people have used against me is Genji or D'Va (because she can deflect incoming projectiles and move faster towards the turrets) but mainly Genji.

Use his reflect to kill the Turret and then flank them properly. The more Genjis you get, the merrier.

One of the most effective counters I've seen is Zarya. Seeing how the turrets have no control to stop shooting she can exploit them and make them charge up her particle beam. Combine this with with her alt fire and recharging shield she can quickly get in and take out turrets and any Torbjörns around without having much challenge.

Personally my choice is Junkrat, but he's my choice for a lot of things. Once you get riptire you can take out a torb camping by his turret along with his turret, and even before that you can use your launch to get you to good positions to bounce your grenades off walls to hit the turrets. They run up on you? Trap. They have a reinhardt guarding it? Bounce behind the reinhardt, or use your mine to knock him elsewhere. This works best on maps where the turrets are around walls and corners and in chokepoints, long range I would suggest Widowmaker personally, though I've seen people do well with Pharah of course.

I played this situation yesterday (on PC)

Enemy team had 5 Torbjörn and 1 Symmetra. I told my teammate to take full snipers. I personally prefer widow but it should works with Hanzo as well. Take widowmaker, only focus for the turret. If one Torbjörn is coming to you, try to kill him but when you have enough time to: Scope, 100%, shoot turret, hide, do it 3 time and even if he repair the turret, it will get destroyed. Always go for the most on side turret. Once you cleared the first, go for the second. If you see a Torbjörn creating a turret, destroy it immediately, in one shot it should be destroyed while in construction. Don't even bother killing the Torbjörn in that case -> no turret for 10 sec is enough to destroy more. If he recreate again, do the same thing, if you are 2 or 3 snipers, they shouldn't be able to construct more turrets. If they want to construct one they'll have to do it a bit more far. So you can move your payload for some meters, then do the same things over and over, win 10 meter by 10 meter, they HAVE TO go back to make more turrets, so it's good for you since the only thing that count is to get the payload at destination.

EDIT:

More of that, I played on Hanamura versus 2 Torbjörn with a widowmaker yesterday, was in attack on site B. Torbjörn can really be useless if you have a widowmaker, once you destroyed his first turret lvl 2, he'll never have time to put one more turret since you one shot it. Please if you see a Torbjörn and you are your team sniper, just focus for the turret! it take one shot to destroy them once you destroyed the first and the Torbjörn will be useless during the whole game. You have like 10-11 second before the next turret so you still can make kill then, but at first you really need to focus for the turret since really few heroes can do something against it.

EDIT 2:

About Reinhardt, it's great when their is one turret (and even their, if other enemy's heroes have mobility, you have to face the turret, and if they come behind, either you let them kill you, either you turn and the turret kill you really fast, so it's not a "long-term" option, it's in purpose to destroy the turret), but if they are multiple, Reinhardt can't do anything about it. I really think that if you have 4 or 5 Torbjörn against you, you should have 2 or 3 snipers, all the Torbjörn will be useless if you focus for turrets, one widowmaker can handle two Torbjörn, so if they have 4 Torbjörn, you take two widowmaker, only focus for turret you'll be 2 widowmaker unable to do anything else, but 4 Torbjörn will be useless too and your team is now 4 versus 2.