My seperated parents can't stand each other, is it wrong to invite both of them to my twin's first birthday?

My mom and dad have been seperated for two years (going through divorce proceedings). When they seperated my mother moved in with my husband and I because she didn't have anywhere else to go. She also couldn't afford to be on her own. They were married for 35 years and both have complaints about their marriage and what one did to the other. My mother hates my dad. To the point I can't even mention his name. I have a relationship with both of them. I try to stay out of the middle because I don't want to have to "choose". For my twins first birthday we had a huge birthday party. There was about 35 people and I didn't think it should be a big deal if my dad attend. I felt like because there was going to be so many people they could just put it aside for 2 hours and enjoy their grandchildren. My dad was fine with that, but my mother was not. She basically told me that if he came she would not. It turned into a heated arguement and she did not come. Four days after the party and us not speaking to each other she moved out. She no longer has anything to do me. She says that she can't believe I would do that to her after everything she has been through with him. They did not have a good relationship. Love/Hate...but their was no cheating or physical abuse or anything like that. They just didn't get along. She says she stayed so long because of security and for her kids. It's been almost a year and I have not seen or talked to my mother. It makes me very sad, angry, and confused. I keep telling myself it was not about her, my dad, or me...it was about my twins. They deserve to have all people who love and treat them great in their lives. Did I make the wrong decsion?