Hello and thank you for using Just AnswerThere are two types of dependents, a qualifying child and a qualifying relative. The five dependency tests — relationship, gross income, support, joint return and citizenship/residency — continue to apply to a qualifying relative. Generally, you may not claim a married person as a dependent if they file a joint return with their spouse. If your daughter made over $3700 and she is over 18 but not a college student then you can not claim her. If she made enough to require that she have to file and she and her husband file a joint return you cannot claim either.
Your grandson is first the dependnet of his parents so if the mother based on her income is required to file you may not claim the child.
Here is a link to IRS publication 501http://www.irs.gov/pub/irs-pdf/p501.pdfThere are many examples of situations like yours that will help you decide if you can claim any of them. Look under the heading Exemptions for Dependents.
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