Probably not. it's complicated, and depends on all the circumstances.
The first issue is where does the father live. If he does not live with you, he cannot claim you, at all, because you are not related. If he does not live with his child (who is related) for more than half the year, he may still be able to claim the child but not for all child based credits. If the child's SSDI income amounts to more than half his support, the father may not claim him. If the 18 year old father is claimed as a dependent on his parent's return, he may not claim any dependents of his own.
There are two types of dependents, "Qualifying Children"(QC) and
standard ("Qualifying Relative" in IRS parlance even though they
don't have to actually be related). There is no income limit for a QC but there
is an age limit, support test and residency requirement. Only a QC qualifies a taxpayer for the Earned Income Credit and the
Child Tax Credit. They are interrelated but the rules are different for each.
A child of a taxpayer can still be a “Qualifying Child” (QC) dependent, regardless of his/her income, if:
1. He is under age 19, or under 24
if a full time student for at least 5 months of the year, or is totally &
permanently disabled
2. He did not provide more than 1/2 his own support. Social security disability income, in the child's name, even if paid to the parent as payee, is considered the child's income, for this test.
3. He lived with the parent
(including temporary absences such as away at school) for more than half
the year. A special rule allows the non-custodial parent to claim the child, if the custodial parent is not claiming the child. But the support rule must still be met.
A person can still be a Qualifying
relative dependent, if not a Qualifying Child, if he meets the 6 tests for
claiming a dependent:
1. Closely Related OR live
with you ALL year
2. His/her gross taxable income for the year must be less than $4,000 (2015)
3. You must have provided
more than 1/2 his support
In either case:
4. He must be a US citizen or resident of the US, Canada
or Mexico
5. He must not file a joint return with his spouse
6. He must not be the
qualifying child of another taxpayer
In addition, the taxpayer must not be claimed as a dependent on someone else's return.
Social security doesn't count
as income, for the income test, but social security money he spends on himself does count as support not provided by you, for the support test. Money he
puts into savings & investment does not count as support he spent on
himself.
The IRS has a worksheet that
can be used to help with the support calculation. See: http://apps.irs.gov/app/vita/content/globalmedia/teacher/worksheet_for_determining_support_4012.pdf The support
value of a home is the fair market rental value, divided by the number of
occupants.
