We go to the same university, I'm 2 years above them, tutored them back when they were in their first year so everyone knows me. They are literally like groupies. I was always friendly and up for small talk with them for the past 2 yrs but didn't really have an interest in them. They are good social proof.

I'm sober from pussy for 2 months now (let's not say dry spell) and started treading the water a bit with some of these girls, not the desperate ones but there are 2 who seem more experienced and chill. Going well so far only reason I'm hesitant is because IDK how close they are to my sister. I already fucked up once a while ago when a girl wanted to make out with me on a party and I said no because I didnt know if she knows my sister.

How to capitalize on this without making drama for my sister? Is there a polite way to say "I want to fuck you but dont let my sister know"?

Attempt to answer own Q: Dont make move, use them further for social proof