Either in or on would work there. I think the option of 'on' comes from the idea of a team-list. I think I'd probably use in, but on is quite common (and perfectly OK).
How interesting. And I’d say from. Is it less common? Or altogether wrong? If it were, say, a basketball team, would it require the same prepositions?
Yes - any team. And 'from' would be OK too - it implies that there are some members of the team who aren't his friends; but it doesn't imply this as strongly as 'his friends from among the team' (which suggests quite strongly that there are several members of the team who definitely aren't friends).