lindapalm has great advice! I would like to add that you may want to crate them separately, at least some of the time so that each dog will have their 'own' space, and so the smaller one will get a break from the other.
Good luck!
I would start by taking your dogs outside more, even if you don't think they have to pee, take them out anyway.Take them to the same spot they've peed on before. I would also take them for very long walks, they sound like they have to get rid of a lot of energy. Make sure you've gotten rid of the odor from the bed and aywhere else they've peed or else they will do it again. Mix a cup of water, 1/4 cup of vinegar, and 1/4 cup of rubbing alcohol in a spray bottle and squirt it on the spot AFTER you've soaked up the pee and cleaned with carpet cleaner.