Thank you for your follow-up, Sondra.
Your son is stuck in an untenable position here. He either has to do nothing and allow them to stay, or seek an eviction. There are only three ways someone can leave the property:
1. By their own choice or consent (which appears is not the case here).
2. Via a court order based on a restraining order
. This is a situation where one person may have threatened of physically assaulted the other, and that person is now in serious fear of her personal safety or safety of the child.
3. An eviction. This would require your son to give the adults formal written notice to quit the premises--such notice has to be at least for 30 days, and should be either personally served, affixed to their door to their bedroom, or sent certified mail to prove notice. Then if they refuse to move, he would indeed need to take her and her mother to court and obtain a writ of possession. That writ would then need to be given to the sheriff, who would be able to serve it and formally remove them from the premises.
My apologies but there are no other real options here--if she is refusing to leave, he does indeed have to 'throw her out of the house' since the home is his and he can demand full use of it. He just cannot personally evict or remove her from premises.
Hope that helps.