People that are a part of your so called 'gang'.
It is often used in the UK particularly London.
Kid: Yo, you tryna fight my mandem?
Kid 2: No I'm sorry. :(
Not an English/ British term, more of a mongol slang for a mate.
Bled, check out mandem they is rizzin dat bare pissy right dere.
Alternative:
Hello Timothy, do you see that fellow over there by the park bench? He seems to be chatting up my sister in law Barbara.
Mandem - A gang who kidnaps kids
e.g. "yo lil timmy you should be scared of the mandems"
just say it it separately, like 'man - dem' and then you'll basically understand.
Junior: ayo look its mandem innih
Tom the white man: what?