ok while i do understand feeling overscheduled, and I definately understand having a child that is off routine and over stimulated by all the craziness, AND I can even sympathize with having in laws that lilke to play games.
But I guess i don't know if your definition of a "party" is different than mine.
I can see the party with your family being a big one and taking some time,
But if it's just your mil, fil, you hubby and son, with some cake and presents, what's the big deal, It will be the same as having a meal with dessert and ds gets a bonus gift or two to play with when he's done.
we aren't talking chucky cheese with 20 other people are we.???
plus you are staying with them anyways. Did you not plan to be there for any evening/ or even lunch meals????
I can see if the day they picked is busy but at that point tell them you'll have to do it at a time of your choosing, but unless i misunderstood ,if you are staying with them and the party is JUST with them,
.........
then the only problem I see is that they don't like your family and are doing their best to still love you and your son, with out having to put up with your family.
That is a legit issue but in my mind that is a lil different than just trying to fit in two parties.
i don';t know I like to keep my groups of friends and family separate so maybe that's why it isnt' a huge deal to me.