en_tn_lite_do_not_use/exo/12/04.md

If the household is too small for a lamb

This means that there are not enough people in the family to eat an entire lamb. AT: "If there are not enough people in the household to eat an entire lamb" (See: rc://en/ta/man/translate/figs-explicit)

the man and his next door neighbor

Here "the man" refers to the man who is the leader of the household.