the IRS doesn't give a hoot about legal agreements court-ordered or otherwise.
in order for the grandfather to claim her, all these tests must meet:
1)1) be the taxpayer's child, stepchild, eligible foster child or descendant of any of them such as a grandchild or brother, sister half-brother, half-sister, stepbrother, stepsister or descendant of any of them such as a niece or nephew, legally adopted child or place with the taxpayer for legal adoption or lived in the taxpayers household for the entire calendar year
2) her gross income for 2019 less than $4,200
3) taxpayer provides over ½ his support
4) isn’t a qualifying child of another taxpayer. A person is not considered to be the qualifying child of another taxpayer if that other taxpayer is not required to file a tax return and that person (1) does not file such return or (2) does file solely to claim a refund of withheld taxes. This exception doesn’t apply when the other taxpayer files a return to receive the earned income credit.
Generally the parent's and especially the custodial parent has first crack at claiming their child. in that case the following tests must be meet.
the child must
1) be the taxpayer's child, stepchild, eligible foster child or descendant of any of them such as a grandchild or brother, sister half-brother, half-sister, stepbrother, stepsister or descendant of any of them such as a niece or nephew, legally adopted child or place with the taxpayer for legal adoption
2) be any of the following a) under age 19 at the end of the year b) a full-time student and under age 24 at end of the year c) ot any age if totally and permanently disabled
3) have the same principal abode as taxpayer for more than ½ the tax year.
4) Child hasn’t provided over ½ their own support
5) No joint return with the exception for a joint return filed only to claim a refund of tax withheld when neither spouse is required to file and no tax liability would exist for either spouse if separate returns were filed
6) Not be a qualifying child of another taxpayer with a higher priority under the tie-breaker rules
if there is a violation of a legal agreement, that's a matter for attornies and the courts.
