Maybe try restricting water intake when they're free-roaming the house? I'd give them a drink and after a certain amount of time (10-30 minutes, depends on your pups) and go outside.
Save the absolutely yummiest treats for going in the right spot, my babies LOVE those smelly freeze dried liver cubes AKA "good potty! treats"
I have the same concern about not wanting to lock them up - but this means that they have to be baby-gated in the same room with me at all times. If I'm not watching her & Nahla sneaks into a different room, she WILL wee-wee inside!