His ex still involved in his family

Ri
Gosh, this is going to be a long story and please be patient with me.
My fiancé (let's call him S) and I have been together for three years, and things between me and him are great. It took me a long time to say yes to go out on a date with him because I had been told that he was in a relationship with his ex (let's call her C), and I don't date guys who are in relationships.
Despite this, he kept asking me out and one day three years ago, I said yes out of the sole purpose to ask him why he was being such d**k asking me out when he had a girlfriend. As I asked him, his face froze and I thought I had caught him in the act of being a douche, except, I hadn't.
Turns out, C, who had broken up with him a year before for another guy, had told all her friends that they had started dating again, except, she hadn't told him, he had no idea.
Because S and C have had a long history together, so when S and I first started dating, I thought I'd be the better person and encourage them staying friends. The only problem was that while I was up for the idea, C was not. She demanded that S chose between me and her; he chose me.
Scroll forwards to now:
Now, I get along with his family, but C has decided that despite the fact that she has moved on, that she still wants to be involved in his family, but not S. She also hasn't told her new boyfriend that she still has contact with her ex boyfriends family.
This bothers me because I feel that if she should be involved in his family, then she should also be involved in his life, something I definitely don't want anymore. Now that I'm pregnant, I absolutely don't want her a part of our lives, I don't even want her to know that I'm pregnant, partly because it's none of her business, partly because she in the past reacted really nastily towards our mutual friend when S and I got engaged.
Am I being unreasonable for not wanting her near me, my future family or my fiancé? Because I once asked his sister not to invite me and C to the same events and she said I was being a bitch about it. Was she right?

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