Would he have killed his parents for me?

Me and my SO have been together off and on since october of last year. Its been a rocky road but we always made it work. Our daughter was born in july of this year. She was 2 1/2 months early. His mother and step dad have been an absolute nightmare since she was born. I had never met his parents until our daughter was born. Whole she was in the NICU I refused for anyone to go visit her before me. She was born via c section and was on a ventilator. Her dad was allowed back to see her. His mother we can call her sandy. Sandy went to the NICU to see her and when the nurses turned her away she came into the room, pulled me out of my hospital bed yelling at me, pulled 2 staples out and reopened my incision. She then demanded a DNA test for her son who repeatedly refused one. I told her not until we talked about it further and our daughter was stable. We finally made th visitation list after a week so people could go visit her. The day she came off of the ventilator sandy did the dna test without our knowledge or permission. The nurses informed us of this but couldn't stop her. Of course our daughter came back as my SO's and she tried to tell him he wasnt the fatger till he demanded to see the results to which she then played it off like she was joking. I moved in with them with my son (from a previous relationship) so that way I could start working and have someone to watch my son. When me and my SO informed her we would be moving out in about a month she kicked me and my son out. He choose to leave with us. An hour later her and his step father took turns calling his phone harassing him and me. We blocked them across all forms of sovial media and their phone numbers. Their response was to change their numbers and continue to call amd texts making various threat such as taking our children, putting us in jail for random things, threatening our jobs, they called our apartment comolex numerous times to complain to the point we got a warning. In the past month we had 4 visits from child services and 2 visits from the sherrifs department to welfare checks on our daughterm never on my son. My SO decided to take matters into his own hands because no matter how many times we notified police or tried to file harassment charges nothing was ever done. He went to their house in the middle of the night and waved a butcher knife at their security cameras. He intended to scare them and not hurt them but he told me if they had answered the door he isnt sure what he would have done he was just so furious with how they have treated me and the kids that he couldnt stand it anymore. He is facing charges for this now because the police finally decided to step in. He tells me everyday he would do ANYTHING for me. But now I am realing wondering if he would have killed them and did it because he thought thats what I wanted. I'm mad at them but have never said I wanted them dead. He is such a kind person and this has shocked me to my core.