Hi there and
to the forums!
Based on what you've described, Sky does sound like a girl, although, as Deborah said, the posted pictures really aren't the best for determining gender as we can't really see their ceres
Also, I noticed on another thread you mentioned Thunder wasn't a "true" albino. Albino budgies are completely white with red eyes and pink feet, if there is any colour on them at all and they don't have red eyes, they are not albino and could be any variety of mutations
For example, if he's mostly white, but still has a pinkish cere as well as some blue on his lower belly and rump, he is most likely recessive pied. Recessive pied budgies have a few coloured patches and are mostly white (blue based budgies) or yellow (green based budgies). The male's cere in this mutation stays pink their whole lives, like an albino
Hopefully you're able to get some clearer pictures of their ceres, as well as chest and wings, if you'd like mutation confirmation!
Anyways, it's great to have you with us around here
Be sure to read through all the links FaeryBee provided as they will be helpful in staying up to date on the very best of budgie care!