One of my favorite advice columnists is Carolyn Hax of the Washington Post. Just today, a reader wrote in, saying that her parents were constantly bugging her 21-year-old sister about who she was dating. The big sister wanted to help and tell the parents to back off. This is what Carolyn wrote:
<<<So, yes, you can be a huge help to your sister, by declining to join the cast of this shouldn’t-even-be-a-drama.
It’s a deceptively difficult role, to relinquish one’s role. You have to fight the very impulse that moved you to write this letter, the voice that’s telling you, “I want to help my sister,” and, “Someone needs to restrain my stepmother.”
But your sister needs to restrain your stepmother, and she needs to do it by helping herself.
If she were making a disastrous choice — if her boyfriend were abusive, say — then it would be your duty to get involved.
This situation, however, like most, isn’t extreme. It may be human nature to see life in terms of highs and lows, but the bulk of it, really, is just navigating the vast, annoyance-flecked stretches in between — without inflating them into dramas.>>>
I think Carolyn’s advice is applicable in the OP’s situation.