My 8yr old son and 6yr old daughter want to share a room. I have 4 children altogether. The home we are in is a 4 bedroom and currently my 11yr old and 8 yr old boys are constantly fighting. My 4th child is only 7mos old and he wakes 3-4 times a night so he can't be roomed with my 8 yr old do to school. My room is not large enough to room the baby with me. I refuse to get him in the habit of sleeping with his father and I. So my question is... In Oregon state is it legal to let opposite sex siblings to share a room? Once again the ones willing and wanting to share is a 8yr old brother and 6yr old sister.

While it is possible, your issue really is making the 11 and 8 year old behave. Go back to the basics and make them learn to live together.