yuo could claim your daughter as a qualifying child if all thse tests are met
• she has the same principal abode as you for more than ½ the tax year. Temporary absences like for school are ignored. for newborns it's from date of birth including any stay in the hospital.
• if she is not a full-time student, she's under 19 at the end of the tax year. If a full-time student, she's under 24 at the end of the tax year.
• she hasn't provided over ½ her own support
• she didn't file a joint return unless there was no tax liability but merely filing joint to facilitate refund of taxes paid in
IRS support test worksheet
https://apps.irs.gov/app/vita/content/globalmedia/teacher/worksheet_for_determining_support_4012.pdf
if you can claim her, the rule is she can not claim her son as a dependent IRC 152(b)(1)
the same tests as above would apply to her son for you to claim him
if you do not meet the tests to claim her then you can not claim the child becuase the parent has a higher prioity under the tax rules
