NTA Your husband needs a support person? Uh, no, he is the support person. Your husband doesn’t get to make demands in this situation because it isn’t about him (even though those are his babies) this situation is about you and those baby’s. That’s it. Those are the only people who matter and whose feelings matter in this situation. The only one who gets to make demands is you… you have to be mentally comfortable and catered to during this. You’re body is about to go through the trials of childbirth times two. So what you say goes, who you want in the room stays, who you want to leave goes. Your husbands brother will have lots of opportunities to witness births during his education and career there is no reason he needs to be in the room for yours. Your husband needs a serious talk to if he thinks he can make this about his “needs”. The only thing he needs to do in this situation is support you and keep quiet.

Good luck OP. I wish you all the best!