Bless you for taking on the dogs, while your friend is at Boot Camp. I did that for my daughter when she went into Boot Camp, and ended up keeping her dog.
I have already told her I will do it again when she is deployed in February, so I imagine this time it will be over a year.
Lots of advice can be given here.... For me it really helped to squeeze another crate in our kitchen and I fed her dog in this crate. Evidentually I switched over the food, so all the pups were eating the same thing.
Also, be sure you are the pack leader, so your little Gatsby feels comfortable with these new additions. Good luck.