few pullets are laying but dont know which one is it

It is hard to tell by looking. There are some signs such as a red comb, but I don't find that real reliable. I also don't totally trust finding one on the nest and assuming she is the one that actually laid the egg. It is a pretty good indication but I've had several that will stay on the nest for a while and no new egg shows up.

I have not done it, but I have read about putting food coloring inside the vent early in the morning. You have to do it every morning, but there will be colored streaks on the egg.

If my pullets start laying before winter sets in, they usually lay all winter and keep laying until the next fall when they molt. If they don't start laying before the days get real short, they might not start until next spring, but mine that do lay seem to lay real well, even in the winter.

Good luck!