Hmmmmm, my dog has a problem with separation anxiety from me, and I know all about how to deal with that. However, with another dog I don't know. There are a lot of knowlegable people here at PetTalk that I am sure will have some ideas for you.
The only thing I can say that would probably help, would be to start separating them a little bit at a time, and then slowly increase the time......I statrted with that with my dog, and it is probably a similar type of problem.
Kedi, Wylie, Rudy, and the dog Scout!