20M here, just recently discovered this and started to actively improve myself. There's this group of girls (from 22 to 25) who work as receptionists at my gym. They for some reason get all giggly whenever I go to talk to them or pass nearby. They say hi to me, ask me questions such as my age, where I'm from, and which one of them I like more (this one I have no idea how to respond, but manage to redirect the conversation somewhere else gracefully somehow).

They give me lots of IOIs, from smiling and twirling their hair; one of them gave me a nickname (a playful version of my name), and she sometimes will brush her hand on my ear when she passes me and I happen to have my back to her.

Question is: how to interact with them as a group and (if needed), interact with the one I liked the most?