AITAH for not inviting FIL’s girlfriend to my husband’s birthday dinner?

My husband has a birthday coming up. He specifically asked to have an intimate dinner with his siblings (including one spouse) and his dad, Aaron (his parents are divorced and he’s not super close to his mom.)

His dad has a girlfriend Lynn who has teenage kids. We are not huge fans of her. The way she speaks is very argumentative as if she’s always trying to defend herself. She also (lightly) forces my children to kiss her and says “well if you don’t give me a kiss then you don’t get pizza next week.” Her own children have no respect for her either for a number of reasons. There are many more red flags including treating Aaron like a child, talking to my husband like a dog (literally yelling NO! at him when he told his dad something she didn’t like).

So anyway, my husband just wanted his family there, but Aaron said “ok I’ll bring my gang with me” and I said that my husband just wanted it to be intimate. Aaron said that he would catch shit for that so he can’t swing that. He says that since the spouse of my husband’s sibling can come then his girlfriend can come too. I feel like he’s choosing this girlfriend over his son.

Let’s also keep in mind that his ex wife left her family for another man. And isn’t that what he is doing? Leaving his kids (even though they are grown) for another family. I told Aaron that she needs therapy if she’s going to be this sensitive. And didn’t tell him he needs to get a back bone.