HELP WITH MOM

Destiny • Two beautiful angels and my rainbow girl!
So just getting opinions on this, I completely support my mother in what ever she does but I am a little leary.... My mother had me at a very young age. I am now 18 including my ex step fathers children (who I refused to believe wasn't my biological dad until I was 11), my biological father's, and mothers children I am the oldest of 11 siblings my youngest sibling is almost 1 I love them all!!! But my mom is now thinking about getting her tubes untied and having a child with her new SO. Me and my fiance are trying to conceive and don't want anyone to know anything until we know the gender of our rainbow baby (hoping we get our little one this month!!). She really wants this and is reconsidering because I am of age to give her grandchildren and her youngest is almost 10. I feel bad because she doesn't want to take a chance of "me getting pregnant on birth control" like I did last time (everyone thinks I'm on birth control still) and us having kids at the save time. I don't want to be the reason my mother doesn't follow through with this. I don't want to ruin the surprise of me ttc. I told her if she really wanted this she should go for it. My worries are more placed on the man though. He just strikes me the wrong way. I feel uneasy around him. I've told her about this but she swears he's perfect. My worry though is her last ex decided after 3 months of perfect amazing "daddy/husband" act he tried to kill her in front of me and my siblings I had to pull my 2yr old sister and 4yr old brother from her before she went through my livingroom wall. So I might just be over protective but I'm worried. Any advice? ALSO I PUT IT IN THIS GROUP BECAUSE ITS A TYPE OF RELATIONSHIP SORRY IF ITS IN THE WRONG ONE.... also I get asked A lot ages are 18,17,15,14,10,10,10, 8, 2, 2, and 11months. 7 girls 4 boys