Escrow Services

[Dales]

Hi,
I'm looking for a flexible escrow service whereby I can use a single 'holding' wallet for multiple users (100s), therefore the 100s of users have the same key, and we have 4 other keys for me and two arbitrators. It would then require 4 keys to release the funds. Is there a service which can accommodate this requirement?
Any feedback would be great.
Thanks.