Is he filing taxes with you every year?
Household in this context is related to taxes.
For example, 3 friends / roommates are renting the same house. There are 3 households in the house.
People who are part of same household typically are: spouses, their minor kids, and/or dependants (say old grandma who cannot care for herself and does not have income).
If you somehow combine income together and pay joint taxes (not sure how), then sure, his income can be used. Otherwise he can be a joint sponsor and fill a form, if his income alone qualifies to sponsor somebody.