Oh gosh, yes, siblings!
In my case, sisters-in-law. TWO of them that drive me bonkers, for very different reasons. One, whom I've nicknamed AIDSIL (angry, in-denial sister-in-law) insists everything is fine, when clearly it is not, habitually acts first and thinks later, refusing to see the consequences of her actions. The second, nicknamed PECSIL (patronising, evil, conniving S-i-L) knows everything about everything and will not listen to reason.
Without going into details, AIDSIL is full of mad ideas, which usually involve trying to create a "normal" life experience for M-i-L (parties, pets, pampering...you get the idea). M-i-L has virtually no short term memory, and is now a permanent resident in a care home, so these experiences are largely wasted on her. Plus, the care home do an excellent job of keeping her busy and entertained in far more appropriate ways. In the past, I have only reluctantly gone along with AIDSIL's mad ideas just to keep the peace, but have learned the hard way that, sometimes, it's best to step back and not to get involved. So when the latest mad idea failed spectacularly (as I knew it would), I felt a certain
schadenfreude when she complained to me that "the responsibility for [the idea] is ALL ON MY SHOULDERS!" (i.e. WHY DIDN'T YOU HELP ME?!) "Awww", I said, "that's terrible!", spoken without feeling a single shred of guilt!
PECSIL thinks it's OK to override everyone's thoughts and feelings and just do what SHE wants. She has taken it upon herself to liaise directly with the local council over M-i-L's financial assessment, even though there are 2 perfectly capable PoA holders who could have done the job (and she is NOT one of them). She believes she can hide certain facts and that they won't come to light. Again, I have stepped right away, so I don't know the details, but I do know that the council are investigating. It's her signature on the form, so she must take responsibility for her actions, is all I can say about that.
So, my way of coping with siblings is to stay as uninvolved with them as I can manage to. That probably makes me an "invisible" now, at least in AIDSIL's eyes!
That's not to say I don't care. I visit M-i-L regularly, and support my OH with various tasks. I do a heck of a lot less than I used to do when M-i-L lived in her own home, for sure, but I reckon I've done, and am doing enough now.
Oh, and by the way, PECSIL gets very irritated with AIDSIL's antics, and AIDSIL can't bear PECSIL's control-freakery, so it's not just me!