Unlocking Origin Island and Multiplayer

Both my son and I have Fantasy Life, and we like to multiplayer. However, I've progressed through the game much further than he has, and I'd like to get the DLC, because I've heard it greatly expands the game.

Listed as the prerequisites for unlocking DLC are: finishing the main story, unlocking two specific party members, and reaching level 50. I've done this, and he hasn't (and has quite a bit to go). There's also a note that says that a game with DLC cannot multiplayer with one that doesn't.

However, I've seen online in several places (like this) that you can get the DLC prior to doing these things, but it doesn't unlock certain things until you meet the requirements. This is somewhat convincing to me, since various sources say it opens up even some pre-postgame content.

So the question is: If both of us get (purchase) the DLC now, can we still play together? I don't want to risk not being able to multi for a while, since I assume that once I activate the DLC on mine there's no going back.