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Based on what you have stated it does not appear that the roommate are qualify as "family" or "household members" as per these 6 definitions.
(c)Adult persons related by blood, marriage or adoption.
(d)Persons who are cohabiting or who have cohabited with each other.
(e)Persons who have been involved in a sexually intimate relationship with each other within two years immediately preceding the filing by one of them of a petition under ORS107.710
(f)Unmarried parents of a child.
Unless the landlord is somehow responsible for contributing to the abuse, there is not a way to break the lease without consequence here. The landlord does not generally have a duty to protect roommates from each other. So, the best course of action here may be to obtain a restraining order against the physically abusive roommate which may cause that roommate to have to move out due to a geographic restriction placed in the order such as the abusive roommate must at all times maintain a 150 foot distance from the abused roommate.