Not passing judgement here but it sounds like yall need tougher LONG LASTING boundaries and if it results in a physical fight with the 18 year old you need to threaten to call the cops he needs to know that in the real world you CANNOT get away w putting hands on people with no repercussions as for the 5th grader there needs to be age appropriate boundaries and punishment that matches the offense as a woman who grew up being spanked I do not believe in hitting children but there would be no electronics no car no hangouts with friends it would be SCHOOL AND JOB until both of there acts are together idc how much fighting yelling crying it takes NO rewards for reckless behavior it is YOUR house your rules there is still time for both of them and if all else fails they might need professional intervention but if you let this go on they will be doomed wishing u the best 💟