AITA for not accepting a stepdad??

So my moms been with this guy for about a yr and they are planning on getting married, whatever. He was cool until we started seeing red flags. The guy seems like a major opportunist, doesn’t see his own kids (grown but still), weird with money and a functioning alcoholic. Not to mention he’s screwed my sister out of money, drove drunk a few times since meeting him, had like 3 or 4 jobs in a yr and hurt my mom (emotionally) then blamed it on mental health to get back in.

My sister and I are both grown and on our own and I have a family of my own with another on the way. My little family has always been close and welcome people into our family always and we were nice to this guy when he came in. Recently he’s been heavy on saying how much he loves us and always wanted girls of his own so he’s claimed us since day one with nicknames and all. He even claims my kids and my unborn son…

To me he lays it on wayyy to thick and I don’t feel connected to him… none of us do. He’s okay but he’s not my damn dad and he’s no grandpa to my kids! He’s weird and overbearing and it feels like we have to love him so my mom will chill. She always says if she can except my husband (who’s very good to me and my sis loves him on her own) then why can’t I do that for her. My mom thinks I’m an ah for not excepting him as such despite everything so aita?

Edit: neither me, husband, sis or the kids are close to him just my mom. We mostly say hi and bye at most if we see him. We are still close to my mom and although my kids are younger forced relationships are toxic so sucking it up and just letting him be a grandpa is not the way to go. The kids have bio grandparents already so they don’t even see him that way. When I say they’ve been together a yr, I mean with a breakup and we barely interact with him. My whole extended family thinks it’s all weird and overwhelming too. I can be cordial with him but it’s the forced family connection I’m not feeling and it’s weird for us all.