For context, I'm 30 years-old. I think she's 35, as is her sister (twins, but not identical). My coworker is married, her sister is not.

My coworker is sexy as hell (not even her body, just generally), and super flirty (not sure if it's just me, but seems to be). Her mother also works at the company (completely different departments), and also seems to have really taken to me. My coworker's sister showed up for an office party earlier this year, and we actually kind of hit it off, and as she and her mother were leaving, she commented that I was "really cute". Considering I'm hugely insecure, I didn't make a movie, and sort of kicked myself afterward.

At some point, I overheard her sister was dating some dude, so whatever, opportunity missed. I've seen her in passing a couple of times, when she was picking up her mother, though rarely had time other than exchanging pleasantries.

Well the other day, my coworker invites me to drinks with her friends (also coworkers). She mentions offhand to one of her friends at some point that her sister was either single again, or was in the midst of breaking up, but either way told the bartender her sister would be on the market again in like a week.

So... I feel like I need to make some kind of a move, if only to prove to myself that I'm not a complete bitch.

What do you guys think? Feel free to ask follow-up questions before giving advice, I'll try to be responsive to every reply.

My gut is... maybe I ask the mother how her other daughter is doing, and use that as a segway to see about giving my number to her daughter? Or is that, like, a terrible plan?

Or should I just not do anything, and if I do happen to see the sister again, make a move then? For that matter, should I just hold out and see if anything comes of my coworker specifically? (not that it should factor into it, but her sister is probably more physically attractive, though something about my coworker just really gets me going).

Any and all replies are appreciated (and yes, being a "beta bitch" is why I'm even sitting here asking for advice).