Would you get involved in a couple's quarrel, would you get involved when a father is reprimanding his own son...
If they are crossing a line and inflicting harm, yes I would.
Couples who quarrel end up settling their problems under the sheet...
Do you mean like domestic violence rapes?
No, in my country saying “the couple solves their problems under the sheets” means that “that's their problem” and if you interfere “it's none of our business…”.