We have a fairly middle ground with PIL as MN goes, but this will be long, sorry.
PIL spend around half the year very local to us, and the other half two thousand miles away at their "other house" (usually two months on, two months off). They took early retirement in 2006.
When they are here they invite our older DC (5 and 2) for sleepovers on a relatively frequent basis, say once or twice a month. This is very lovely for them but doesn't really represent much of a "break" for us as they've only just started taking DC2 now that we also have newborn DC3. They keep both DC up late - DC2 to 8.30 to make him sleep through reliably, and DC1 past 10pm so they can spend time with him, and in any case they don't want to have to come home from the pub before 7pm to have their tea. Again, that works out nicely for them, but gives us two completely exhausted and difficult children when we get them back.
I realise that some/many people get no nights off at all and many children have no relationship with their grandparents at all, so I have learned to count my blessings and hold my tongue and be grateful for what they do do. Equally, I don't rely on them at all, so all my back-up plans (eg emergency school pickups) are based on friends and not the PIL. We sometimes invite them for Sunday dinner, they sometimes invite us, they came to the nativity last year, etc.
But DH is starting to feel that this is unfair. PIL were able to retire early because of the jobs they had had while DH and SIL were growing up, which they could only have because GMIL provided free childcare (wraparound during term, full-time during holidays). I try to point out that everyone makes choices and nobody was held at gunpoint etc etc.
Matters came to a head this weekend. DC1 had been begging for FIL to come to his football practice (Sunday mornings) for some months. Since he was at PIL's on Saturday night, DH and FIL agreed that FIL would deliver the DC back to football instead of our house in the morning, and stay to watch. DC1 was extremely excited about this.
FIL didn't even stay for long enough to see DC1's boots tied, because he said he had shopping to do. DH then had to entertain DC2 during the session (we normally keep him away as it bores him) so couldn't watch DC1 either. FIL asked DH to lie to DC1 and say he left just before the end.
At the end of football DC1 asked DH if FIL had left straightaway. DH admitted that he had. DC1 cried.
DH is now absolutely raving. We have a strict no-lying policy with our DC and he refuses to lie on FIL's behalf who couldn't be bothered to put his shopping off for a few minutes to watch his grandson playing his heart out.
DH wants to go round to PILs' tonight and basically have it out with them. He's fed up of being put upon (constantly providing free IT support, lending out our garden equipment, providing lifts to and from airports, etc) without getting the benefits in return that he sees SIL get (lots of house renovation DIY stuff, free holidays, etc). He has been tipped over the edge now by our DC getting second best as well.
I don't think this would be remotely helpful. I think it would upset DH even more without actually making the slightest difference to how FIL and MIL behave. They've obviously justified all of it to themselves and enjoy their life. When DH and FIL argue, it lifts roof tiles. PIL are going back to their other house shortly so there's no chance to talk through things calmly and sensibly and reach agreement before they go - just a half-hour row and a lot of bad feeling.
I'm right to persuade him against a showdown, aren't I?