If you are able to catch/slip them out from under mom at night, that is a very good time to weigh them!
I love
@Ponypoor 's idea - that works great! And, the cloth bag that holds them kinda snugly but not restrictively will keep them mostly calm.
I was thinking a small container that you could slip a piece of mesh or cheesecloth over to keep them in...and set on your small digital scale should work fine.
If you have removed the dividers in the broody cage, you should be able to slip a hand under Tassels after dark and slide a little one out from under her...wear a lady's soft leather glove and a long sleeve shirt if she is still aggressively pecking.....
Digital bathroom scales won't be sensitive enough for such a small bird to do this with and have any accuracy.
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Obviously, any Roo at your place also needs a royal name given he is living in a Palace with royal women....so here is some thoughts (but, I am sure you can think of others, too!)
Royal male names
Knights of the Round Table.
I am partial to Sir Lancelot!!!! Tee, hee, Hee