When can a taxpayer claim a minor sibling as a dependent?
First of all, the parents should not be claiming the dependent! Here are the 4 tests that the IRS will look to establish whether or not a taxpayer is entitled to claim a sibling.
The dependent must be brother or sister.
The dependent must have the same residence as you for at least half of the tax year.
Age. The dependent must be under age 19 at the end of the tax year; under age 24 and a full-time student for at least five months out of the year; or totally and permanently disabled.
The dependent must not have provided more than half of his or her own support during the tax year.