Search Results: getting married after 3 months

My sister and her boyfriend recently got engaged. Right now, they have a beautiful baby, she's 9 months. They've been together for about 6.5 years.
I'm happy for her, and wish her the best.
But 1 thing that always extremely bothered me, is how her now fiance used to make strange comments to me.
He'd say things like "I met the wrong sister. I wish I would've met you first." I'd tell him to stop because I didn't want him hurting my sister, and it was really uncomfortable and disturbing. He'd tell my mama, "how would you feel if I left the daughter I'm with for the daughter I want?" She'd get mad and tell him that he was being disrespectful to both of us. I remember I was also learning to drive, and he said he wanted me to sit on his lap "in a non sexual way" just so he can "help me steer". I got angry and told him no, that was completely disrespectful. He'd also constantly invite me out to eat with him, I asked him why. He'd say because he was trying to get to know my sis family, but he never asked any of my other siblings, just me to eat with him. I'd refuse. He would constantly tell my mama yet again, how he wished he met me first. And told me if I'd ever give him a chance, and I said hell no. 1. My sister loved him, so no. 2. He dated her, so no. 3. I don't like him as a person, so no. 4. I don't find him physically attractive, so no. 5. I'm not into the Jerry Springer/Maury drama of stealing my loved ones bfs. I also don't condone cheating, especially on my relatives.
This was like from year 2-year 5 of their relationship.
Why haven't I told her yet? Because she loves him so much. My brother worked with him and told her he didn't think he was trustworthy. She got mad and told us to stay out of their business.
Sorry for the life story, but should I tell her before they get married or after? I don't wanna ruin their chance of getting married, but I don't want him to hurt her either. I love my sis but this has been bothering me for some time :(