This daughter sounds extremely selfish and spoiled big time. She wants her dad to pay for the wedding but insists on excluding the love of his life because they are gay?
No thought is given to how the conservative in-laws would make her dad very uncomfortable. Never mind committing the ultimate transgression against his spouse by saying "we don't want you there."
It's pretty simple. If she wants dad to pay for the wedding then her dad's spouse should be warmly welcomed. Period.
If the in-laws-to-be can't cope with that, THEY can stay home!
The person who pays has the right to bring whomever he wishes to bring.