Hekt the Monad will accept mithral medallions, which can be found in giant severed heads, in exchange for Wondrous Items. She will be cheerful and welcome the party to her underwater library, at least until they figure out they need to destroy Hob.
Alice and Bob will accept platinum medallions, which can be found in burning severed heads, in exchange for magical armor. They will seem greedy for the medallions.
Oswin Oswell Oswald will handle all interactions with visitors. He speaks with a robotic voice. The party may exchange adamantine medallions, which can be found in belching severed heads, for magical jewelry.
Gorwin the Gardener is the most public of the Quintet. He maintains a small garden of living plants. The Quintet will exchange alchemical items for gold medallions, that can be found in screaming severed heads.
Zazel will greet visitors and inquire as to their reason for visiting. He will trade magic weapons for silver medallions, which can be found in grabbing severed heads.