While I have five dogs total in my house it isn't a situation I would recommend. Unless you're very structured in your home life and how you manage your dogs you're only going to mess up a service dog by placing them in a home with other dogs.
I think the only reason I manage is three of my dogs are working soon to retire stock dogs who live a very structured life, a service dog and service dog in training. My dogs are not allowed or encouraged to play with each other and they're never left loose when we're not home. All the interaction, play and enjoyment they get from me. Service dogs are not pet's and while they need time to run and play and be dogs you still can't treat them like pets.