Holding Deposit Contract

[Meleana Tuimoala]

I held a deposit for 3 tenants (room mates) on a unit and only one of them signed the deposit. It was $1600 deposit and $500 non refundable. One of them is asking for a refund of his portion he gave to the roommate that signed the holding deposit. Am I obligated to return his portion even though he’s not the tenant that signed the holding deposit? We are first time landlords and are still learning with all these new situations that have been coming up.