S.H.
I'm sorry, but I'm not really sure what your complaint/problem is.....
sure they've said/done some really weird stuff....like the Vegas/take the kids off your hands...comment. But....are you just venting? That's the end result of my reading your post twice now!
I totally get their "no" to you today...about you going out for Mexican instead of picking up the kids as scheduled. Late or delayed pickups drive me nuts! They had plans, they were going out.....I totally get it.
As for the whole not eating thing....it really doesn't make any sense. They overfed the baby? & didn't feed the 6yo? Don't get it! & how did picking up the kids affect your dinner plans....again, don't get it! If your 6yo hadn't eaten too, then the reasonable choice would have been for you to pick him up & then go out as a family. If the baby was full, then he would have been content thru dinner!
A lot of your post just feels like somebody complaining. It seems as if no matter what your ILs do....you are going to find fault with them. I'm sorry if this offends you, but I don't know what else to say. They are gparents, they are not responsible for childcare. They have nights out in their lives, they travel, they give you $$.....so what if they don't feel a need to babysit? This does not make them "bad"....& life should not be a competition btwn the 2 sets of gparents. One set enjoys baby time & one does not. The End :)