I want my mom and sister but I feel guilty

I have had a huge crush on my mom (f49), and an even bigger one on my sister(f24), for years. I want to do such taboo things with them and I always think about it while I do my thing. The only one I really think would ever possibly do something with me is my mom but even that’s a stretch. The biggest issue is the fact I have a girlfriend whom I adore and I love so dearly, so I feel really guilty about all of this. Sometimes while we have sex we do a slight mommy role play and I can’t help but think of my mom and sister during it. I never want to hurt my girlfriend nor will I break up with her, so I don’t know what to do about these feelings.
I also don’t want to cheat on her, but when I’m masturbating I tell myself that it’s not really cheating since it’s with my family, and I couldn’t get in a romantic relationship with them. That makes me feel bad too afterwards. For context my mom is divorced and I live with my dad and stepmom, and my sister is married. I’d love it if my girlfriend did like incest but I’m scared to say anything, we’ve known each other for a long time but only been dating almost 6 months. I’ve asked if she wanted to call me daddy (I’m not into that but I just wanted to know) and she said no she didn’t like that. Also when we’re doing the mommy stuff the most it goes is me calling her mommy and her calling me her bb, along with the usual dirty talk. Plus I know I’m kinda hypocritical because I wouldn’t like/don’t like to think about her doing any of that with her brother or family.