oh man here's the trick.
-you break the ice whatever way makes more sense. You open either girl. Based on circumstances it may be the girl you like, the other girl, both at once, or you might not be sure which one you like yet
-you focus a fairly equal amount of attention on both of them at first. So they both feel included. unless one is naturally more checked out than the other. don't force anything, but still do your best to loop both girls in to a certain degree.
- you lead the conversation by involving both girls. if one girl says something you ask the other girl "is that true" or "what do you think about that" "what about you" and so on.
-okay now this is where you start baking your next moves into the process. You start asking one girl about the other girl like "you know her pretty well, what do you think? you must find her creativity pretty inspiring" things like that.
we'll get to how this step is important in a minute, but first this next step
-once you have momentum you subtly focus your attention on the girl you like. Get into a little bit of a bubble with her. not totally blocking the friend out, but just letting the convo naturally move towards the two of you connecting. A little more focused eye contact, more focus rapport between you two.
maybe you loop the other friend in once or twice so she isn't neglected, but you keep the focus on you two.
- Once there is a high point you qualify her on something like "hey I like your attitude, that's a keen observation"
-okay remember how we set a precedent of asking the one girl about the other. You ask the friend to qualify the girl for you. so you turn to the friend and ask something like "hey she's pretty smart, I bet she's a pretty great person to share a coffee with isn't she?". something around those lines. Note that you are not asking to take her friend out or something, you are asking a qualifying question. "hey I bet she's great company over a drink. wouldn't you say?"
Basically if the girl you like is subcommunicating interest, and her friend notices this, her friend will give the stamp of approval of qualifying her friend to you "yeah she's super cool". that sort of thing
-Then you just suggest to your girl that you'll grab her number so y'all can be in touch. Depending on the dynamic you will either just suggest it as you and your girl meeting up (like if the other friend is pretty hands off in that moment). Or you can suggest in a way that is an invitation for all of you to be in touch, but since the precedent has been set that you are hitting it off with the one girl, the implication will be that you and her are the connection point and it will make most sense for you to grab her number either way.
So you just hand your phone to her while you suggest meeting up, or better yet you have her hand you her phone so you can put your number in. then let her know your gonna shoot yourself a text and type "hey cutie

Samantha (insert girls name)" (shout out
@Skills for this number close)
also important to note is that after her friend qualifies her you might not just jump right into the number close. see that qualification as the stamp of approval, and then let the conversation naturally segue before closing. It could be right away, but also it might take a couple more conversational beats. Again, it is ideal try to aim for high note when going for the number close.
Keep the convo going just a bit longer with both of them as you grab her number and wrap up the interaction.
There is no need to be ambiguous about your intention and grab both girls numbers. Sets the wrong frame.
Be bold and memorable by making both girls feel welcome and engaged, but being clear about who you would like to connect with again.
also in two sets, I like to playfully tease them when when I ask I question to them both and they give different answers. I'll be like "uh oh, we got conflicting answers here. I thought y'all were best friends. you got a get on the same page" that kind of thing. This is especially good when it relates to how/how well they know each other. like is one says they're best friends and the other hesitates.
likewise I like to praise them when they are super synced up with each other. things "dang this is so real team work" "wait y'all literally reading eachother minds right now, this is crazy". that sort of thing