Don’t give your opinion unless asked, and if asked just say something simple.
It’s not your job to teach them a lesson or hold up rating cards. They’ll work out their issues on their own, there’s probably a lot more to it you don’t know or want to know.
You can’t choose your family so just keep smiling
I agree with "Mount Athos" - I would only add, don't feel obliged to attend events you don't want to and don't feel obliged to send cards, etc... Don't advertise your feelings, just play dumb and avoid them if they upset you.
I had a family friend who turned "gay" after being married with 2 kids. Then he met another man, his "true love." I didn't say anything. Some went out of their way to welcome them, etc... Then he broke up with that guy, and moved to another, then another, then another. Those who chose to celebrate his first "new love" probably felt pretty stupid after the 3rd time. I started to find him and his boyfriends annoying, unstable and disagreeable people - I happen to believe it is closely linked to their lifestyle, but anyway, the decision to actively avoid them became easy.
Point is - they have chosen to venture out with lifestyle which is usually does not "succeed." So be polite and dumb, but make them prove to you they are indeed "just like everyone else." Maybe they will surprise you, maybe not.
I had a similar situation with a gay cousin. When he was in the closet, he was tolerable. Once he came out and started bringing the boyfriends around, he (and they) became unbearable. He’s recently taken to sending out Christmas cards with pictures of him and his boyfriend sitting on Santa’s lap. Fortunately, I forgot to give him my address the lat time I moved and I don’t get them.
My liberal brother used to take his kids over to the cousin’s house to show how open-minded and progressive he was. He started noticing that every room had phallic symbols all over the place... gay art, gay nick-knacks, gay coffee mugs, gay ashtrays, etc.... and then his kids started asking questions. That’s when the visits stopped.