What is the setup being used that prevents the escrows from accessing their individual keys? (not that this would prove anything without the RedeemScript. I'm just curious)
Right now, Copay multisig. Plenty of wallets don't allow trivial access to individual keys, which includes hardware wallets. You'd have to derive them using some tool, which IMHO compromises the seed.
Also, is it a possibility to send a trivial amount from the escrow address(es) to a specific BTC address to prove ownership?
This is indeed possible. There is only one BTC escrow address.