Father in Law guest list

My fiancé’s parents broke up when he was young. My fiancé never understood much about why until we recently became engaged and a family wedding was on the cards. Long story short his dad holds bad blood for his mum claiming she was a cheat and owed him money. It makes me and my fiancé angry that his dad is using our happiness and wedding to bring up bad blood between him and my fiancé’s mum. To help with the wedding my parents are paying a big amount, my fiancé’s mum is also contributing and we’re also borrowing some money - my fiancé asked if his dad would contribute a few hundred pounds to the wedding to help pay for his guests (guests his dad immediately insisted on who neither of us know, as my fiancé grew up with his mum, the number he wants to come would cost us a fair amount to cover) . His dads reaction to my fiancé’s request re money was that he was insulted he’d been asked to contribute, throwing a tantrum and immediately threatening to not attend as that’ll save us some money. We’re both aware that this isn’t really about the money though, it’s because his dad feels hard done by that his mums family will very much be present and that he can’t invite all of his. He is now demanding that he gets to have as many attend as my fiancé's mum, which is a huge amount as she has a very large family. Unfortunately his dad also didn’t treat my fiancé well as a child either so I’m becoming increasingly annoyed at his bitter and childish father, my fiancé is also really upset by his dads threats, even though they aren’t hugely close it still hurts him. What would you advise/do in this situation? Thank you X