I'm doing taxes as head of household can someone under my family do it as head of household under the same address?

no

IRS generally does not accept two head of household at the same address
I know it can happen but you are opening yourself up to an audit

This is a guaranteed audit. Proving that there are two households in one is extremely difficult because you are already sharing the kitchen and bathrooms. If you or your children also share bedrooms, living room, cars, food, etc, forget about it.

It becomes a sticky situation and difficult to do. It depends on who is the other person in your family. If you have 2 actual households set up under one roof, then yes. You must not be supporting anyone in the other household. If it is a boyfriend and you are sharing a room, then no.

No you cant.

No, as it's impossible for two people to have paid more than 50% of the expenses.