Abby: Obviously has Adelaide as a housemate. Does she do history classes? Mel is the resident history professor at the university. Archie will be friendly; Sofia will be... less so, because Sofia is prickly.
Lucas: Mel and Archie both know sign language. Sofia... does not like cops. I'm seeing a pattern here XD
Val: Has an Archie, obviously. Possibly knows Mel via the bank, because he is a (very) long-term client of theirs?