How did you get on at the vets today? It's always reassuring to have a vet check. The can sometimes look a bit leaner as they grow longer. If he had parasites he would probably have some bald patches and have scratched raw in some places. I also used to worry about this when I saw Charlie grooming so much but they do groom a lot and scratching is part of that.
It's a shame the little hammy is deaf but he clearly has a loving, caring family. I hope the vet gave some good answers today - let us know how you get on.
Someone else might have better advice about the hoards
There is more than one way to do something and some depends on your hamster's personality as well.
It was so very sad about Mr Crumble but I really think there was nothing you did and it must have been a genetic thing he was born with - a lot of these things are breeding and genetics. Hamsters have eaten all kinds of awful things and been perfectly fine as a one off. One dog biscuit wasn't going to do that. It was just his time - and very sad when it was so soon.
Does Cookie like chews and chew sticks? Four weeks isn't long for him to develop lots of habits and when they're babies they sometimes don't even pouch food at first - that's something they develop later. He's just finding his feet probably.