Should I be this upset

So I just found out that my fiancé’s sister has been taking the pics I send her and the pics I post on my Facebook of my two kids, and sending them to my fiancé’s ex girlfriend. I’m livid. I feel like it’s such an invasion of my privacy and a violation of any trust or respect. This ex of his used to try and “cause problems” by messaging him on Facebook until we both blocked her and because we blocked her I guess his sister has been showing her his life and children and even pics of me, since I had our first child. She’ll take pics of my kids on my profile and make them her profile pic so the ex can see it because if she just posts it to her page I always tag myself in it so the ex can’t view it.

The amount of effort his sister is going through to invade my privacy and for what?? What is her goal here? I haven’t confronted her yet. Another family member sent me screen shots proving this is true to let me know because they were just as bothered by it. I want to block her and never let her around my kids. They are her nephew and niece but she’s toxic and I don’t want that around my family.

I need some comments from y’all on what you think because I have no one to talk to about this right now and I’m fuming

Edit***

I haven’t told my fiancé yet because he tends to take his family’s side with everything and I’m not looking forward to not having any support. I could be wrong and he’ll take my side but idk yet. I also found out that a family friend of mine has been taking the pictures of my kids too and sending them to my birth mother who I cut out of my life because she was extremely abusive to me growing up. What the fuck is wrong with people?? Absolutely insane that two people who don’t even know each other are doing the same awful thing to me and my kids.

This is what I said on Facebook to address it but I didn’t tag them