Am I terrible?

So I’ve started seeing this guy… let’s call him C. he’s adorable. Cute, sweet, and perfect for me. We mesh so welll, I feel like I’m waiting for there to be a catch. But there kind of is… I used to like his brother, we’ll call him M. I didn’t realize C was the brother of M (although I should have realized) and nothing happened between M and I, but I’m pretty sure I remember asking him out… fast forward to now, C and I are dating, officially. And I really like him. But I can’t help but think about how much his family isn’t going to like me because of that. Do you think I will be seen as a “homie hopper”. I don’t think C knows that I used to like M. And how do I get rid of that attraction for M? I don’t want to be with M, as I really like C, but wow, they’re both beautiful. And to complicate things more, I used to work with their mother and definitely used to over share about my personal life with her (she was like a mother to everyone). Can I still have a good relationship with him with all of this happening? Any advice welcome.