You don't say how old these dogs are but my advice would be the same anyway probably. Have a schedule and STICK TO THAT SCHEDULE. Dogs like ritual and consistency. Walks and potty should really be two different things (my opinion) -- although going to the loo can certainly be an aspect of the walk. Here, both dogs are expected to go out and go potty when I get up. That takes care of the immediate need. They know that they have to hold it all night and they also know that when they see the whites of my eyes, they get to go out. Most of the time, Bo will also poo at this time. Bea not always.
The morning walk is a different thing. The focus is not bathroom --- although it can occur -- it's exercise and fun (for them) and leadership (for me). Bea uses this time to do her poo-ing before we begin our walk ritual.
Why don't you try breaking up those two events?