I pretty much know who is who by how they jump up or how they feel as they jump up.
Kit will usually trill when she jumps up.
Piper is the heaviest of the 3 who gets in bed with me usually before I fall asleep.
Molly doesn't usually come until the middle of the night and I wake up with her ON me somewhere. But if she jumps up when I'm awake, I know it's her as she'll also trill but in a different tone than her sister, Kit.
I also know who is who by the position they settle in.
Kit will snuggle up next to my side if I read for awhile, but moves to the foot of the bed when I shut the light off.
Piper will lay on my legs pelvic level for some pets before moving to the foot of the bed, where Kit sometimes will give a big hiss at her warning her not to snuggle if she isn't in the mood.
I also know who is who of these three by feeling them. All three have a different texture too their fur.
My fourth girl, Philly, prefers to sleep alone downstairs.