I need some advice

I’m 7 months pregnant and my boyfriend which is the father of my baby had a previous marriage and had 2 daughters. Well we had a really rough relationship though out my pregnancy we broke up a couple of times and those times he went ahead and had sex with his ex . I took him back tried to just move on from it and I’ve been okay and haven’t been getting involved in their co parenting . She hates my guts so bad and has disrespected me and my son . So me and her don’t get along . Well now his older daughter which she’s 5 asked him to go trick or treating with them which is w his ex as well . I told him I do not agree and I feel uncomfortable and disrespected. I told him I wouldn’t mind if he just takes them or if I either go to . Am I wrong for this ?