Two are 6 months old (neither crowing yet, both silent in fact), three are just over 5 months (Visby croaks first thing in the morning, the other two have that sort of squeak between a cheep and a bawk, but Lulea's close to crowing I think), and three are one week younger (of them, only Merioneth yet crowing, the other two squeak). So same sort of age that you expect them to start crowing.
yes, though RJF are just bantam sized aren't they?

And as I understand it, they form smaller nuclear-type flocks, unlike my mixed largish flock.
I'm sure you're right that crowing serves multiple purposes.