Note that there are three fundamental requirements, to claim an unrelated person:
• he lived with you the entire year.
• He had less than $4200 gross taxable income
• You provided more than half his total support for the year
Nontaxable Social security disability 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 does not count as support he spent on himself. If you provided a home it helps your support case, unless they own the home you live in. If no one person provides 50% of the support (for example his children are also sending support), then a "multiple support agreement” (IRS Form 2120) can be used, to allow you to claim the dependent. https://www.irs.gov/pub/irs-pdf/f2120.pdf
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.
