Gayle Inge and her husband, Miochael Inge, said Thursday that Zander should be returned to them.
Ingue is Zander's legal guardian under Florida law. Last month, McCready took the child out of Florida without court permission.
The singer and her son were found in Arkansas.
McCready told The Associated Press that she took the boy because she feared he was being abused at her mother's home. Gayle Inge has denied the allegations.
The boy is currently in the custody of Arkansas child welfare authorities. The Inges say Arkansas shouldn't have jurisdiction over the case and that being away from his Florida family isn't in the boy's best interest.
The Associated Press contributed to this report.