Relatives I haven't seen in years... How to deal with family pressure?

Can you pull the venue to small card? Honestly I would dig a little deeper as to why your mother hates these extended family people so much. Chances are there is more to this story. I would not want to invite family I don't even know the names of.

You get to decide who you invite to your wedding. Sounds like your mother needs to get over it. And yes ask for specifics, than you can weigh whether or not you think its important enough to not invite them over.

Is your dad paying at all? What about mom?

Is your mother paying for the wedding? Is your father contributing?

If you are paying 100% of this wedding, you get to choose who you invite. When other people's money gets involved, they do kind of get a say.

It's so weird. My mom is paying for most of it but my dad is going to contribute. Initially my mom didn't want him to contribute at all because she was worried he would start making demands, so for her, this is her fear. I don't really see this as "a demand", he never said I had to invite them, I just kind of assumed they would because they're family, even though I never see them. I didn't realized his family was such a sore spot for my mom because she never talks about it...

Sounds like your mom might have a little manipulative blood in her too. I would let your mom know that you would like to invite them and explain why (if there's a reason) and see what she says. If you've already accepted her money (and his), you can't ignore her opinion but hopefully she can recognize that it's still your wedding.

You get to invite who you want to invite.

I would ask your mom for a deeper reason as to why. I know someone who got divorced from an abusive husband, and his family slandered her, prevented her from getting jobs, was rude and mean, and so there may be a deeper reason and perhaps their treatment of her post divorce. Honestly, unless you truly think your mom is being dramatic and catty, I would respect her request. She will always be your mother and it sounds like you barely talk to your dad's family. Not worth making your mom feel anxious the whole day to please people you never see.

Thank you guys for all your advice, it sounds like my parents and I just really need to sit down and talk about it (Probably not all together). When it comes to this sort of thing there is no right answer. I really appreciate your thoughts!

Something similar happened to me. I told my dad that I was not planning to invite my aunt, his oldest sister. He pushed, said I had to, it was important to him. I knew, to me it was not going to make a difference if she was there or not, as I don't have any adult relationship with her and she has not been to any "family" gatherings (holidays, graduations, etc) in a very long time, and she never met my fiance at the time.

I gave in, sent her a Save the Date. She replied that she would not be going. Simple as that, no reason, told me all about her helping with her Grand niece's wedding on her husband's side, about her summer plans, her trips to Mexico, and blatantly said "no we are not coming."

I knew, like you probably do, that you have no adult relationship with these cousins and that it would do more to cause discomfort for those you DO really care about, such as your mom. You can try to explain to your dad and be honest - you don't have an adult relationship with these cousins, you will try to accommodate them to the best that you can, but can make no promises.

He should respect that, this is not his event, and understand you will do your best to involve everyone but that might not be 100% possible

I think discussing it with your parents is best. Perhaps yuor mom has a sotry she hasn't told you about why she is so upset about them potentially attending. Although they are family, if you don't want to invite them, you do not need to. I personally wouldn't bother inviting them if I don't even know their names.