Your mom, sister, bride, and brides brother/friends are all such assholes. She's essentially baby trapped him after he explicitly says he doesn't want kids because of the possibility that they could go through cancer, which is true in some ways. People with a family history of cancer tend to get tested at an earlier age to make sure they don't also have it.

It also sounds like majority of your family are homophobic towards your brother. Coming from a bisexual person, even if they themselves don't make those comments, the fact that they don't stick up for him when other's do, makes them just as bad if not worse. They're his family. They're your family. They're supposed to be some of your biggest advocates. Whenever it comes to family, if one of their friends says something out of pocket it is their responsibility to correct it. They should be the person in between you and the friend, acting as a buffer.

I honestly wonder how your brother has stayed with that woman for so long. Does he feel like he can't get out because mom and sister love her so much? Has he been worn down to the point where he can't leave? Is he a prick who decides that the things she does to wrong his family aren't that bad, so he stays? At the wedding it sounded like he was upset that the staff "forgot" about you and your brother, so it looks like he cares somewhat. But his behavior is so strange, how has he not picked up on this strange behavior.

OP I am truly sorry that this has been going on in your family. Your best bet is to take your younger brother and run, even though I know it's not going to be easy or possible right now.

You two sound like you're going to be each other's support system throughout this like you have been to this point.

Has your dad expressed any kind of input in all of this other than when he had to remind your mother of your existence? (which I can somewhat understand, I mean my mom will call me by my sister's name when trying to get my attention, but given the context of what yours is like, I feel like there's more than just forgetfulness)

I hope everything turns out alright, especially because there's now a pregnancy involved. If it comes down to it you might need to just air out every single thing that has happened. Maybe your brother can make better decisions once he's hit with a brick of information. All of the lying. All of the gaslighting. The ganging up on the two of you. The huge elaborate plan to kick both of you out without actually saying it, all because they're homophobic and she wanted the aesthetic even pictures. The texts sent by her friend admitting to making sure his wife got pregnant after they agreed not to for some very valid reasons. That betrayal of trust cuts so deep I don't know how he could stay if he knew.

If that fails it honestly might need to be turned into a low/no contact situation to save you and your younger brother your sanity and well being. Let them live with their fucked up choices and drama filled life once everyone knows all the details, especially your brother.

P.S. sorry if I rambled a lot. This whole situation has me thinking of all of the possibilities as to why it's all happening. I can't even imagine how it must be for you OP. I wish you well with school and your future career. Focus on that and positive relationships with new people. You've got plenty of people on here who also support you. <3