Alright managed to escape for a bit.
Toileting can be very frustrating thing to solve.....especially when you are not there. First of all i will go through some basics that i find usually help.
1) Do they have access to an area outside? Often if they can get out when they need to they will stop messing. I find doggie doors brilliant to use for my dogs and they do pick up the idea quickly if they are shown how to use it.
2) Are they both entire? You may find that getting them both desexed may help the problem
3) Are you using a deodouriser after they make a mess. Smell is such a big part of dog's habits so make sure after you clean up there waste (and put it in there toilet area) use a good quality deodouriser like SOX or Odourex.
4) Can you leave them outside when you are away. If you can then it will make the problem go away very quickly.
I think we can try a gradual introduction to the house to make sure the problem is controlled as we go.
Put both dogs in a crate in a warm, quiet room. They should stay in this room at all times including feeding (other than taking them out regularly to toilet). This will limit where they can make a mess in. Make sure if you catch them making a mess to tell them off and take them to their normal toilet spot.
When you arrive home make sure you take them out straight away. And the same idea before you leave.
Once they have survived in this room for a week without messing then they can be let into the next room. Every week they are well behaved they get a new room until they are perfectly trained (thats the plan)
Some other ideas are to feed both dogs where they mess.
I would also suggest using a a product called DAP that can help with problems like these. Set the diffuser up in the room they will be limited to.
Good luck with them and make sure to keep me up with what is going on and if i can help anymore
Todd