@Enemias, Title 26, IRC A.1.A.I.2 Defiles Head of Household under section b (1) A as follows--> ( only those items applicable to the case at hand :(
1. In general for purposes of this subtitle , an individual shall be considered head of household if, and only if , such individual is not married at the close of the taxable year, is not a surviving spouse …...
(A) Maintains as his home a household for more than one-half taxable year the principal abode , as a memebr of household of
(I) a qualifying child of the individual ( as defined in section 152(c)) determined without regard to section 152(e) .....
Section 152(c) defines Qualifying child as:
(1) In general the term Qualifying Child means with respect to any taxpayer , for any taxable year, an individual--
(A) who bears a relationship to the tax payer ….
(B) who has the same principal place of abode as the taxpayer for more than one-half of such taxable year
(C) who meets the age requirement s....
(D) who has not provide over one-half of such individual's own support ….
(E)who has not filed a joint return .….
Thus in my considered opinion, your father definitely can claim Head-of-Household with the proviso that he meets all the conditions called out above.
The purpose of the special rules for divorced parents (Section 152(e) ) is for the express purpose of allowing divorced parents to equitably access/ distribution of the dependency ( which requires residency ) , child credit, EITC etc. and has nothing do with whether a child can be a qualifying child of one or the other parent.
The requirement for parents to live apart for at least the last six moths of a year is for the express purpose of the inclusion of parents who are not divorced but live apart ( considered un married )
The fact that two single parents live under the same roof ( while may be unusual ) and with their children, cannot be used against them , at least for tax purposes.
I rest my case
