Joint sponsor/household member

hi I am a uk citizen engaged to a usa resident my question is my fiancé lives with her mothers boyfriend, her two children and two blood related uncles. They are all claimed on taxes by her mothers boyfriend since they all live together. She does not file taxes has she has no income. So, my question is could her mothers boyfriend be a household member or not? He does not make enough to be a joint sponsor so that is out of the question. Since he claimed everyone on his taxes would he be a household member or not?