Freezing, thawing, then freezing Is this ok to do. I have 3 beaver that I thawed out to flesh tonight, but realized that I don’t have any nails. Is it ok to freeze them again?

Flesh them then freeze them until you get some nails.
You could also keep the fleshed skins in a cool place for a couple days no need to re freeze unless it is going to be 4 days or more until you find some nails.
If you have a staple gun you can use that instead of nails to board them.

Greg Schroder did a demo when my son took trappers ed where he taped a fork to the front of the staple gun it leaves your staples up just far enough that they are easy to pull when your hide is dry.

yes