Thank you, they are my first chickens so learning lots, from what I've read (and youve confirmed) how they look/ behave I'm sure 5 are cockerels, suspected hen looks very different, smaller, head is lower, and as you said comb is barely visible.
I will try & sell / sensibly home the cockerels first, failing that I'd quite like to try dispatching myself (keeping one, how I will decide who I've no idea)

Does mean I'm going to have to look for a couple more hens, will start my search shortly for some girls around the same age, hopefully easier to bond when still young?