lol, I happened to spot it.
I'm not sure why one is brown and the other isn't, my best guess is that they are not the same species, or perhaps one is a different morph? As for male or female, they may be to young to tell. Generally once they reach sexual maturity, the cloaca of the male will be much larger and prominent that on a female. I'm not sure how big FBNs get... I'd say at least 5 inches.
It's good you bought them. They are awfully thin. Make sure you get them good and plump.

Also, try a good variety in their diet. Newts eat alot of grubs and things like isopods, so try things like isopods (rolly pollies), waxworms, red wiggler worms, phoenix worms (black soldier fly larvae), etc. The waxworms will help them put on the weight, so you can feed them somewhat regularly for now, but later when they are in better health the waxies should only be a treat.