The guardian is claiming because the family is dysfunctional they do not deserve to have a gathering after the funeral. She also already broke the contract made
originally by the eldest daughter with the funeral home. The second son has
just died. Now there are only 2 remaining daughters. The Mother has a large
family who loves her and would like to honor her. This guardian is out of line, I believe by making a judgement against a family she doesn't even know.
I think you should follow what your parents wanted but think you should also try to get the guardian to state her position in writing, then forward it to the judge who appointed her and state that you feel she's overstepping her boundaries. If she's billing for the time she's objecting to the funeral, there's no reason why your family, or whoever guardianship was appointed for, should pay for that kind of unwarranted intervention.
However, Willie raises a good point. On whose behalf does this guardian act? Was it your brother? If so, I agree that the guardian shouldn't have any more rights or obligations.
Sorry to be so blunt, but who's interests are being served by the different sides of this disagreement?
Prayers and best wishes!