@witchfynder_finder for the IRS etc, all the information i have seen is that a household is limited to spouse and dependents; for other things uhhhh i've never really gotten a good answer
your parents are effectively roommates in this scenario so??
@witchfynder_finder the number one thing i want to change about forms is making them stop asking for gender information but RIGHT BEHIND IT is getting rid of all the assumptions which expect a nuclear household