Yep, I agree, asking, "What are you going to do about it" is a slippery slope. Any questions (as a method to guide them) could be a slippery slope. This invites the opportunity to offer advice/opinion, and in this situation, opinions and advice should be avoided. The second you offer advice and/or opinion is the second you become the heartless <blank>, and it may not be that way now, but this is the sort of thing that rolls around and bites you in the butt later. It also opens the door to *having* to volunteer to take the burden off their choices. Do not open that door. Not with these people. Just "mirror" or "echo" and empathize. Don't "stray from the script."
Your job at this point is to let them express their frustrations should they express them to you. Once they have a chance to vent, they may clear up their own mind-fog and see their own choices and own solutions. Of course, you don't want to be the brunt of unreasonable ranting forever. At some point, you may have to say, "You've been complaining about this for months/years. I think you need to fix it. I don't want to hear it anymore." (or something to that effect)
**Pee or get off the potty/get off the cross, someone needs the wood/you made your bed, you lie in it -- are proverbs that come to mind.
I'm not sure the situation at Easter was an intentional, personal slight, but I can certainly see that the OP is suffering the consequences of her (perfectly reasonable) choices. There is always backlash. Things get worse before they get better. Just don't feed the trolls.
It would be perfectly easy to just wash your hands of the whole thing. It's so easy to say, "I will have nothing to do with these people ever again," except for the fact that this isn't an easy, black-and-white situation and it isn't just YOU. There is a spouse involved here and other extending, blending relation-ships, some of which you would like to maintain. I'd like to see how well it goes over when the wife (husband) says, "I will not have anything to do with your family ever again." It's not that easy. How about we figure some polite ways of managing these difficult situations, especially at the family dinner party when the OP was seated next to "the enemy" and her husband was "planted on the opposite side of the country." Divide and conquer? LBM is sort of the forgotten and unwanted extension? Put her in charge of baby care so we can talk with the important one? Or was it just a lot of poor planning and there were no ill-intentions at all; it just turned out to not work well and no one spoke up?