MIL problems

So long story short ever since my soon has Been a baby baby my fiance and I have been dealing with his mom, his sister has a daughter that is 5, and a 8 month old girl, his mother literally constantly watches them all day, and I with i was kidding. Sometimes it's because they both work, most times his sister and her husband are lazy. His mother practically raised the 5 year old and it's the same as the baby, my fiance's sister is over at her house constantly with his mom changing, feeding, bathing, everything to those kids. His mother shows them love and affection constantly without a doubt, but when it comes to my son she literally DOESNT CARE. it breaks my heart, she will only watch him maybe a few times a month but never willingly, and when she does there is ALWAYS a problem.

Last Wednesday she told us she wanted to take him Sunday because she is going to have the girls and the oldest wants to see my son to play, so we agreed and made plans to work around im the house and have our time together. So Sunday morning my fiance called her to ask when she wanted him, she made plans with his sister and her kids to go to his aunts house🙄 ( his aunt is a whole different story knowing we don't care for her and don't want our son around someone who doesn't care about him) she said he can come too if you want him too.

I got super super upset because once again she put him last. She never sees my son and she lives literally 20 mintues away and she couldnt have done it before Sunday?

We didn't have our son go with her that day because of how we felt, my fiance constantly went through that when he was little and felt like shit and let her know that.

This stuff constantly happens with her.

But now she's asking to take him tomorrow for the play date. I don't wanna take him away from them but i don't want him to go through that, he's little enough now to not understand.

What should we do???

Were we over exaggerating???

Im just tired of it.