Sounds like a messed up family to me. I do know that some dogs get overly excited if there is fighting... not sure if they feel they have to defend the Alpha or what? We only had one incident involving a dog of ours. My teen son was playing with his youngest sister and picked her up to put her on his shoulders. She was giggling and screaming but the dog seemed overly tense at that moment. He was interpreting the screams as one of fear and not laughing. Once I stepped in, it was over but dogs see things differently.
My parents had a disagreement, nothing serious, not even raised voices, but their German Shepherd sensed the tension and moved between them to sit in front of my mother with his head cocked staring at my stepfather. The rest of the day he stayed very close to mother.
Funny thing is they seldom disagreed and never got very heated when they did but that day the dog noticed some tension, did not like it and made them aware that he was there to defend and protect his mistress.