So, here is the situation. I am not very close with my mother. She and my father divorced when I was too young to even know what was going on. It was a very horrible breakup with very long court proceedings involving custody battles and a LOT of legal fees. My Dad ended up getting full custody of both my younger sister and I. We visited with our mother every other weekend and one night a week up until we were teenagers and had a bit more say, at which time we mostly chose not to visit much at all. My father remarried over 20 years ago and this woman spent most of her time helping my father to take care of us. I would not say that to me she represents a "mother" figure, more like a cool aunt. I feel like I have never really experienced a true mother-daughter relationship.
Fast forward to budgeting our wedding and discussing guestlist/financial contributions from family. My Dad has always intended to contribute a substantial amount, but he has always said that my mother would need to contribute as well, since she has in no way contributed financially to the lives of me or my sister EVER. Well, I knew this was never going to happen, though I did think maybe she would offer something (buy me a pair of shoes, veil, something not too costly). When we had the discussion with her as per my father's request, she firmly said that she could not afford it. Nothing, not even $1000, literally nothing. The ironic thing is that she is vacationing (alone) in Florida right now for three months to escape our cold climate. Of course it is her prerogative how she wants to spend her money, and many people get married without any contribution from their parents. We are very lucky, and if my Dad contributes what he has intended then the split would be about 1/3 him, 1/3 FI's mom, 1/3 FI and I. We truly do not NEED any contribution from my mother, but my dad insists that she needs to pay for something if she wants to attend. Every time we see eachother he insists that she is not coming, though I have never agreed to that or let him think I ever would. We may not be close, but she is still my mom, technically, and I do not agree with not inviting her to the wedding. However I am worried how this decision will affect my relationship with my father and I'm not sure how to get him on my side on this. He has resorted to attempting to reason with FI and implore HIM to speak with my mom instead and attempt to encourage her to contribute. I know this is wrong, we don't even need whatever extra money she could provide, it's just the principle for my Dad. Is there any way I can resolve this situation without someone being mad/bitter with the final decision? I don't want any tension to arise on the day of the wedding.