Social media appropriateness with the ex family?

My husband’s ex wife has a close knit family, she has three younger half sisters who my stepsons 19M and 21M are close with, especially Aunt “Nicole” who is the cool wine aunt who lives in a cool city and has her own company and promises them internships and access to her apartment but never follows through. The ex wife insists on the kids being with her for every holiday because her father hosts things and thus I’ve never had my stepkids for any holiday from Easter to Christmas but that’s besides the point!

Aunt Nicole has repeatedly tried to follow me on Instagram. My profile is private because my husband’s ex wife and her family were lurking on my LinkedIn and I generally just wanted to keep my instagram life private anyway.

I have never met any of the half sisters. I’ve met their father who is one of the nicest people I’ve ever met, probably due to his own experience with divorce and his most recent wife being a stepmother to all the grown daughters.

My husband’s ex wife has (according to my stepkids) usually spoken about me in very biting terms, with a lot of sarcasm and self deprecation to bait a compliment - think along the lines of “I bet chimes320 doesn’t burn the dinner she makes YOU”. I feel for these kids, but I never ever ever say one word about their mother. I’m not sure what she’s said about me to her family but I’m a little uncomfortable that her sister keeps trying to follow me. This is strange, right? I’ve literally never met her, and will probably have no reason to until the kids get married someday. I am just ignoring it for now but this is the second time she’s requested to follow me, it’s … not appropriate, is it?