Thanks for posting your question. Although I'm not a doctor, and therefore cannot give you any medical advice, I do have herpes and I think I may be able to help you.
The quick answer to your question about contracting herpes from a roommate would be: no.
The long answer is: I'm sure there may be a slight chance of catching it, like, if the roommate has an outbreak on his butt, sits on the toilet seat, then your friend sits on it right afterwards and has a cut in the very same spot. Sure, MAYBE it could happen, but the toilet seat isn't exactly the best breeding ground for the herpes virus. The disease would not survive long in such cold, dry conditions. I've never heard of anyone getting the disease from a toilet seat.
As for "sharing towels and wash clothes" (?), there could be some danger sharing a dirty towel with the roommate. If the roommate has an outbreak, uses his towel to dry himself, then afterwards your friend uses his towel before it's been washed, the disease could potentially be spread. But if they are sharing towels but washing the towels in between the sharing, then there is no way it could be transmitted via the towel. I have had herpes for several years and have shared towels with roommates (washing the towels in between) and with family (accidentally not washing the towels in between) and have never passed it on to any of those people. As for washing clothes together, I don't see how that could transmit the disease either. So I guess the point is to practice good hygiene and don't share towels unless the towel is washed between different users.
In response to your other questions: yes, you can be tested before ever having an outbreak. You can get a blood test done. If the roommate only has genital herpes, and not oral herpes, you don't need to worry much about your kids. (Just give them clean towels! Every child deserves a clean towel!) :-)
In short, you don't have much to worry about, unless you aren't practicing good hygiene. It's okay to share clean towels with the roommate but not dirty ones. Again, I have had numerous roommates over the years and am confident I have never put any of them at risk. I'm also very careful and conscientious of my personal hygiene.
If you want more information, you should check out Genital Herpes Basics, Prevention, and Causes and Risk Factors.
Hope that helps!