How can I securely generate secret-sharing/multisig keys on a p2p network?

How can I securely generate secret-sharing/multisig keys on a p2p network?

I am trying to create a peer-to-peer escrow system. I need to encrypt the private key of a wallet with a 2-of-3 secret-sharing function - the buyer, seller, and arbitrator will each have have one key.

The problem lies in the generation of secret keys on a p2p network, as there is no trusted server. What can I do to prevent a maliciously modified client from making a copy of the keys before distributing them to their rightful owners?

Thanks in advance!