Hi
Glad you could join the flock! When they first start laying they can and do produce differing eggs untill they get their laying machines in correct working order. If your girls are healthy and acting normal I would not be worried about the differing egg sizes for now, once they get going they should produce normal eggs regular for you. As for the Christmas lights I would turn them off. They don't need to see at night when they go to roost. That is their rest time and when they digest the food in the crop. You only need supplement lighting if you want them to lay eggs in the winter when the daylight hours are reduced. About 14 hours per day for light and they should lay well. Having lighting on as pullets could be pushing them too quickly into laying. I find it best to let them do it naturally and at their own rate.
Even though your chickens are the same age they will not all start at the same time, they're all individuals. Usually the more red the comb the closer to laying they are.
Wishing you the very best of luck and enjoy BYC