Hi Jess,
Training multiple dogs can be fun or really frustrating.
I always recommend spending time working individually in multiple dog households. With my three dogs, I take them on walks individually sometimes to work on behaviors such as leash walking and off leash control. I also think they enjoy a bit of quality one-on-one time.
It is always ideal for dogs to be comfortable in other rooms alone so you can work with the other dog without barking interruptions. You can also put dogs outside, if you have a yard and work with the other dog.
You can also work up to more advanced strategies such as what I do with my dogs. I have them all stay and call one dog to perform a task while the other two maintain the stay. Then, I send the one dog back with the others, call another and work with him. This has taken a lot of time to get to this point, but it was fun.
A product that you might enjoy is a DVD by Patricia McConnell and it talks about multiple dog household strategies.