I died and can't respawn

For some reason your spawn point has ended up in midair. It might be a bug but it's more likely your brother did it as a joke.

Either you need your brother to fix it or you need to find a way to survive the fall, make a bed and move your spawn. This would probably require you to log in as someone else or persuade someone to put water under your spawn point.

Have your brother find your spawn point, then start building a platform to catch you when/where you spawn.

If we're talking PC version there's probably some console commands that could be used to move your spawn point to something that isn't a high-altitude drop. I'll leave explaining those to somebody who knows what they are doing though.

follow up with CrusaderJ's answer:

if you are on pc, you can enter a command. if you die with the chat window open, it will remain open until you enter something, which means you can change your spawn point. (assuming you have the permissions to)

you can enter something like the following:

/spawnpoint (your ign here) ~ Y ~

explaing the command:

/spawnpoint sets your exact spawn point, so you always spawn on the same block. it only effects one player.

(your ign here) this is your in game name. replace it with whatever your ign is. mine would be thedudxo. this tells the console who's spawn point it should change, in this case, yours.

the first ~ is a Tilde. it can usually be found on the top left of your keyboard, under the escape key and above tab. press shift to get the tilde. this ~ represents the x co-ordinate of your spawn. since we don't need to change the x, only the y (height), we can set it relative to your current position (ie. it won't move your spawn on the x axis).

next we have Y. this represents the height of your spawn point. we need to replace this with something closer to the ground, but not under ground or you will suffocate.

if you are above something like a hill, it should be about 70-80. if your above a flat area it should be 65-70. you will have to experiment to find what works.

remember, below 64 will likely have you in the ground.

the final ~ is the same as the first, except it represents the Z axis.