Personally, if I'm gone that long, I hire a young adult, usually who's still living with mom and dad to come house sit for me. I like to have someone there with my animals and monitor the house. They typically like the break from mom and dad, too, and I'm more comfortable all around.
I admit I waited to leave the dog until he was almost 3, and I did make sure it was someone that could handle a GSD. But I also had a labrador that I trusted implicitly with the cats. I know Rocket wouldn't hurt the cats if I were gone that long, but I wouldn't want him alone without any human there for a week.
How is their relationship? Do they sleep together at night? Lay together during the day? Or do the cats only tolerate or even dislike the dog?