I feel for you, & can relate to a lot of this with both sides of our DDs GPs
though my parents live a long way off, & now both have serious health issues, so can be excused, & TBH, despite my relating to a lot of what you say as regards them never visiting etc etc....mine have never visited any of my homes either, not even when I have been seriously ill & in hospital, yest can manage a 300mile round trip to loaned my Brother money 
these days they blame Mums ill health, but I know it would be the same regardless, as it always has been that way with me, so I doubt DC would make any difference.......& yes on challenged on this or any other issues Mum sounds EXACTLY as you describe.....but will blame my being "the coper" & therefore my Brother NEEDS her more 
that said, they have actually made more effort than MIL, in that on visits to them, on a couple of occasions, when DD was younger, they've told us to go out for a meal & they would watch her, we had to be near by, & contactable by phone though, but better than nothing I suppose.
despite my otherwise getting on well with her....MIL on the other hand is a complete joke, she makes a big deal of DD in front of her friends, wants the gossip on whats shes up to etc, so as to have something to talk about with them, but despite her living not too far away, I can still count on 2 hands the number of times she's babysat
She would only watch her when she was older.....god forbid she might have to change a nappy
& partly because I got fed up with the fact that she would only watch her here..of course AFTER DD was in bed
this meant her staying over.....& she also expected to come early & have her tea cooked for her
had to be by me too
.....& then she would be up at the crack of dawn....6 am is a lie in for her, & then she'd let herself into our bedroom, wake us up & then sit on the bottom of the bed chattering away as if it was a perfectly normal thing to do 
We have tried insisting DD stayed with her instead....did it once & the phone calls started at 5 am asking was DH on is way to pick DD up & if not what time
she insisted DD was fretting for us & wanted to go home......DD denied this saying Nana had told her to say this 
SIL is good, but childless & has a very full social life, so generally just not available on weekends but will gladly do a week night, but sadly doesn't work as DH has a very early start for work 
So having been through it, I can TOTALLY understand your frustration, even though DH & I generally have a great relationship, I've even found myself on occasions a bit envious of out split up friends who share care of their kids 50/50, as they get whole weekends off
but realised that the old adage of "you can't change others, you can only change your reaction to them" is very very true, you'll just wind yourself up trying & stewing on their inadequacies,
so don't waste your time & energy, it will get you nowhere....just set yourself up with a group of other Mums in the same boat, & swap sleepovers etc, your kids will love it, the other families are probably just as desperate as you, so you'll win all round :)
good luck :)