I'm the kind of person who would read the "fine print" from the brokers (Schwab/Fidelity...Years ago Morgan Stanley). I would always see the words "at their discretion". Don't know if that is still true...
firstly Etrade doesn’t link PM accounts with futures accounts. While I have been margin called a ton with Etrade, I never let them auto liquidate. That is super dangerous as it’s an indiscriminate market order. I would think they would liquidate at random as there’s no such thing as the one position that put you over. It’s all just a bunch of positions in a limited sized basket.