Sorry for the delay
This will come down to he court order. If your wife died and she was the primary custodian, the court will need to decide if the 22 year old can be the legal guardian.
Someone needs to raise the child. By default, this would fall to you...but if your wife wanted her daughter to raise the child...the court can consider this request. And if the court finds that the sister is best suited to raise the 15 year old child, the court can grant this...the court can give your daughter custody/guardianship
of your 15 year old.
If this happens, you can expect that the court would continue to require you to pay support...the amount would likely be the same as you have been paying...if not more.
But this presumes that you do not wish to raise the child yourself. If your goal is to raise the child and you tell the court this, its not likely they would give guardianship to your daughter.
Please let me know if you have further questions; if so I will do my best to answer them. If not please hit the accept button, its the only way I get credit for my work.
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