I'm new here so I'll give a little background:

Fiance has lived with his parents since his divorce. He left the house to his Ex so their children would have a home to live in. Ex let the home go into foreclosure, moved into a condo and has primary custody of the kids. Fiance's custody is everyother weekend. Child support is based on him having them every other weekend. He carried medical/dental, pays 75% of all medical/dental balances, pays 1/2 of all extra curricular activities for all children. Pretty basic. Fiance's drivers licence, bank records, etc. all have his parents address as his primary residence, however, he lives with me, (I own a home) about 85% of the time. There is less than 2 miles between my home and his parents. When he has his children for the weekends, he stays at his parents so they can see their grandparents. Fiance's parents LOVE me.

Here is my question:

Should fiance and I just let it go when it comes to MY FIANCE'S parents paying birthmoms portions of unpaid bills, extra curricular activities, extra's, etc. for the kids? My fiance's parents CLAIM that they cannot stand his Ex, however, they give her money "for the kids". This really bothers my fiance. They are HIS parents. She has her own parents who live close by. She has family AND she should be supporting her portion of her children. Yes? Please keep in mind that the Ex DOES have the children a majority of the time, but child support is based on that. AND the Ex pawns the kids off on Fiance's parents. They allow it. So in actuallity, Fiance has them every other weekend, the grandparents 1-2 times a week and the Ex the rest. An example of why my Fiance gets upset is this past weekend Fiance's parents INFORM him, don't ask, INFORM him that he needs to chip in some money for his children's school clothes. His parents decided that THEY were going to take the kids school clothes/shoes shopping and that Fiance needed to shell out some money for it. (I call BS on this-I think Fiance's parents and the Ex were in on this and discussed this without Fiance's knowledge-this is what hurts Fiance's feelings and pisses him off) So the grandparents look like the hero's here buying the kids clothes, then behind the scenes they are demanding money from Fiance. This happens ALL the time. One of my fiance's boys did NOT want to play football this year. Fiance's dad talks his son into it, PAYS ALL FEES IN FULL, says HE will take care of everything, then demands that Fiance drive son to and from practices. When fiance refuses, his dad gets extremely upset and treats him like a deadbeat dad.

My honest opinion of this is that Fiance is living with his parents and they feel like they have some sort of hold on him and can have a say in the way he does things and runs his life. Am I right?

Opinions and advise please.