littlestlily... Sorry, I didn't mean to make you think that you'd done anything wrong in asking your PILs for help. You SHOULD be able to do that and a normal set of PILs WOULD. Imagine, not even helping out when their own son was in hospital? It's completely unthinkable.
I'm just coming at the problem from the perspective that it must be grating and soul-destroying for you and your husband to even have to garner up the request for help from your PILs in the first place, only to likely be refused. I just couldn't. They seem to have no familial feelings whatsoever and I can't imagine anybody in a family behaving like that under any circumstances.
What would I do if it were me? I would put PILs on a 'do not contact' list as far as I could. Not a 'going no contact' (unless that is what you want to do?), but a general arms-length, don't contact them at all arrangement. I would then be looking around my family and friends and explaining the scant (and it is scant) help that you/I need and the circumstances it would be needed. And there I would have my back up plan.
The flipside will be that PILs would not be invited to any dinners, days out, any nice grandparent style activities. Do it all with your own parents and nice sibling(s), any other family/friends in the wider circle who would like to be closer to you all.
I've never been in favour of tit-for-tat in families, ie. you don't help our kids/we don't help when you're old and need it, kind of thing, but I'm totally in favour of that for you. Disregard them as far as your husband can comfortably stomach. That would be my advice.
You sound a very nice, close family... don't let your PILs lack of warmth do anything to taint that, they really don't deserve to matter and your children are not enriched by their involvement with them anyway.