Can you file as head of household when separated, not divorced, when claiming one child as a dependant?

My son and daughter-in-law are separated and have been for over a year.  They have three children and He had the children for half of the year.  She is claiming the two girls and he is claiming the son.  Can my son file as head of household?  He will be claiming his son as a dependent.
    Yes, it sounds like HOH may be an option. 

    Here are the requirements for filing HOH.

    A.  To claim head of household you have to be unmarried or to be considered unmarried. You are considered unmarried on the last day of the tax year if you meet all the following tests:
    1. You file a separate return.
    2. You paid more than half the cost of keeping up your home for the tax year.
    3. Your spouse did not live in your home during the last 6 months of the year.
    4. Your home was the main home of your child, stepchild, or foster child for more than half the year.
    5. You must be able to claim an exemption for the child. However you can meet this test if you cannot claim the exemption only because the noncustodial parent can claim the child.

    B. You paid more than half the cost of keeping up a home for the year.

    C. A "qualifying person" lived with you in the home for more than half the year (except for temporary absences, such as school). However if the "qualifying person" is your dependent parent, he or she does not have to live with you.

    • I have been seperated not divorced and i filed head of household w 2 dependents. all got approved and refund is coming this week.... good luck ;)
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