http://monerotoruzizulg5ttgat2emf4d6fbmiea25detrmmy7erypseyteyd.onion/resources/user-guides/multisig-messaging-system.html
So in Alice's signer list #1 will be Alice and #2 will be Bob, while in Bob's wallet it will be exactly the other way round. There are three ways to complete signer information: You can enter it manually, or you can use the auto-config mechanism that the MMS offers, which has a second, "semi-automatic" variant.