The whole "giving NPCs" how we (my spouse and I) have made it work is got to camp/tell her to "meet us at camp", then once there have you recruit her.
We made that work, so fingers crossed for you.
So, is it not possible to play your own customized character without being the host??
Is it impossible to play with friends, each of us with their customized character?
In order to play with friends in multiplayer with "your own" character, you all have to be there for the creation of the campaign (i.e. everyone is creating or re-creating a new character).