I'd tell Colin's Dad to step up and be a Dad. Since he and your sister later got married and the kid lived with them under one roof, that piece of paper ain't crap. As most are written it isn't a promise to take them. It is they can go live if them if needed.
Besides that the with Colin being 14 the court and a whole lot of other people will have to sign off on it. Tell Greg not to let him in the house unless he is really considering taking him on. If he does and the court and social services already sees he is living there it will be really tempting for them to leave him there.
