How do I handle my inlaws? They have said they will alwasy be closer to their granddaughters vs their grandson?

I have 2 boy and one girl. Seems like my daughter gets all the invites, cool b-day gifts, and sleep overs, and so on. She is 13 and my boys are 11 and 5. There is another granddaughter that lives with them, and I kind of understand why it is my daughter that goes over there more often (cuz of the girl boy sleep over thing), but recently my daughter got invited to disneyland and i told them my son would enjoy it too. My mother in law says there is a lack of money, and I said.. I will pay. She kept coming up with excuses, so I finally told her how unfair she is being. She wanted my daughter to keep it a secret from my son! She has been a bit distance since then, since i didn't let her take my daughter (they took their live in granddaughter). I am torn between taking away the opportunity from my daughter, but then if she goes, my son will be hurt. My 5 year old still is hard to handle, but my older kids are good kids! Any advice is welcome... Thanks in advance