I live with my mom and right before I went to work, my sil and brother showed up to drop off their dogs because they are going on a trip. While I was talking to my brother upstairs, I saw my sil slap one of their dogs to try in get him to calm down. Not enough to hurt the dog but hard enough to make a faint slap sound. Ive known my sil for a long time but we aren’t close so idk how she would react. I’m not gonna confront her but more like just talk to her and ask her to stop. Idk much about how to train dogs. What I would do is just tell the dog to stay and if they did, give them a treat. Not hit them.