Hi, I'm Robert and I'll be helping you with your computer question.
Do you mean that only one machine can get to the internet through the express router or that only one can use the time machine on it?
is it always the same device or does it switch but only one at a time can use it ?
I may be gone for the afternoon but i will be back to work with you later tonight or tomorrow. I would not normally do that but it looks as if nobody else was giving you an answer very quickly so i wanted to at least let you know that i would help you when i get into my office.