I have a brother that I'd like to join me in playing D&D but I think it sucks that he'd have to spend money that I've already spent to have the same experience. Is there some way I can share with him the content I've already paid for?

Yes, create a campaign and have him join, them turn on sharing content.

Quote from Metamongoose >>

Yes, create a campaign and have him join, them turn on sharing content.

This, but note that you need a Master tier subscription to share content.

Or, you can just let him use your computer the same way you’d let him use a physical book.

That's fair, I guess I could just have him make a character on my account, seeing as how you can have multiple character sheets open at once.

Quote from Duxell >>

That's fair, I guess I could just have him make a character on my account, seeing as how you can have multiple character sheets open at once.

 To let someone else use your account is a violation of the terms of service.  You could make a character for him and provide him with a pdf or a printout, but to have him log in on your account is not allowed. 

What if it's a household account, in that they still live under the same roof?

Quote from MidnightPlat >>

What if it's a household account, in that they still live under the same roof?

 It’s still a violation of terms of service, unfortunately.  

Quote from ArwensDaughter >>

Quote from MidnightPlat >>

What if it's a household account, in that they still live under the same roof?

 It’s still a isolation of terms of service, unfortunately.  

 It is not, because no one has, will, or considered doing such things. We are just having discussions about options in a fantasy game.