The Form 8962 instructions for those Married filing separately are worth noting.
Right, you cannot get a subsidy if you file "married filing separately." There is no reason to file separately and it will not help you as all household income must be included no matter how many people are actually on ACA marketplace insurance.
Yes and no.
All household income income does not have to be included, if one is not married to the other person in the household.
Oh, right. Good point! But in the OP's case, filing taxes separately will not help with ACA subsidies. Rather, it will disqualify them completely from subsidies.