Barry has two younger brothers that I am aware of. The younger one was Dale, and I've forgotten the name of the older one.
I think the older one went off to live with his dad. I can't remember why the younger one went; maybe the same reason.
Unless the brothers are in trouble with the law, I don't think they'd have any reason to creep about and hide. But Gareth almost certainly would have good reason to keep his presence secret.
By the way, I don't think it was Gareth who knocked down Kylie (she would have recognised him anyway), so I don't think the person that Barry has just apprehended was the knocker down of Kyle either, i.e. there are at least two mysterious strangers vaguely lurking around.