I know there are people who use safeguard during molt and have never had a problem, but if they could see before and after pictures of one of my hen's tailfeathers they might be a little more cautious (beautiful pompom tail to floppy, bedraggled looking thing). There are definitely far worse...
A few scraps are totally fine (wouldn't want to deprive your chicks of all the fun and excitement of treats 😉), just wanted to be sure they had a balanced diet, which it sounds like they do!
As for Valbazen, there is no official withdrawal period because it hasn't been studied because most...
It's hard, if not impossible, to keep free range chickens completely free of worms, and normally chickens do just fine with a light worm load, but when you start seeing worms in the poop that's a sign that a chicken is struggling.
I'd worm them with Valbazen.
You could also use Safeguard but...