This occured during my first marriage. As my wife's mother had this great big rambling house she had asked us to move back in after her youngest daughter had moved in with me. Considering that my then mother-in-law was one of the greatest people I had ever met and we would be on the opposite wing of the house and we were both in college, I considered the positives far outweighing the negatives.
A unique nature of the family, 4 adult sons and 3 adult daughters, was the different relationships. The oldest son was a former Marine, fellow gun enthusiast, and a lawyer. He and I had talked guns and he was glad that someone was at the house that he believed would "look out for Mother". Some treated their mother's house as the home of another person and respected all the protocols and some treated it as a completely open house with no part anyone's particular turf.
While I was studying alone one night that nearly got one of them shot! I heard a door on the other wing close and knew that my wife and her mother were not expected home for a couple of hours but nothing prevented them from coming back early so I went back to studying at the desk. Shortly after that I heard footsteps coming up the steps through the solarium and realized that they were not my wife's or her mother's. I pulled a Browning patented Colt .32 from the desk drawer and put the magazine in and chambered a round and waited. The sound of the person moved not to the great room but into the hallway of our wing and I lifted the gun and sighted it on the door. The door opened and without announcement the one person that should have known better, the oldest brother, walked into the room. I identified him instantly and moved the gun to the open desk drawer while calling out his name in a very exasperated and nervous tone. He looked at me, noticed me removing the magazine and emptying the chamber, and just nodded. He grinned and said that lucky for him I hadn't shot him. I told him that it wasn't luck and that dead, not shot, would have been the result if it hadn't been him.