My family is stalking my ex


Today I found out my cousins have been stalking my ex, the father of my daughter on social media. I don't care about his life or anything (we have zero contact) and I've been in a serious relationship for a year already. Well, my nosy cousins kept asking me for information over my current relationship and I didn't want to tell them anything about what's going on/our plans for the future and I guess it pissed off my cousin. So then he went off and started telling me about how he added my ex on instagram with my other cousins (I checked and it's true) & how his new daughter is so much prettier than my daughter. He was talking about how the new baby has lighter skin than my daughter & a prettier nose. I havent talked to my daughter about her step sister but my cousin went off and started telling my daughter she's a big sister, I was so angry and told him to stop but he kept going at it. My cousin is in his early 40's I'm 22 and I don't understand this immaturity. I'm so angry... I left his house immediately. I see him every week due to my parents business (he works for them) I don't know how it's going to go when I see him but I want him to leave my life alone... how would you deal with this??