Another thing that can help is this:
Look for the little nub where the urethra is (where they pee from). If its a female there will be a little drawstring shaped hole (thats the vagina) right below it.
If its a boy, you can see the little nub where the urethra is, but there will be absolutely no sign of a hole there.
That can be a useful tool to use for sexing rats as well.
Photos 1,2,3 and 5 look like girls to me (lay person opinion) but photo 4 its a bit hard to tell.