However, "household" and "house" are two different things. Although it's unusual, two separate families sharing one house CAN at times both claim Head of Household. It would depend on the specific facts and circumstances of each case.
<a href="
http://www.irs.gov/pub/irs-wd/1998-041.pdf" rel="nofollow" target="_blank">
http://www.irs.gov/pub/irs-wd/1998-041.pdf</a>
