Children custody

My Niece having issues with her Husband, who works in Saudi Arabia. He is in Pakistan at the moment, expected to travel to SA on 20th August.
He insist to take their 4 children with him to SA. He alleges that mother is not mentally sound and cannot take care of the kids, therefore, he has to take them to SA. I tried to have a dicussion with him, but he said I have no rights to stop him. Even though it is my niece who doesn’t want to lose her children on such grounds, when there is no medical record available to prove the Husband’s allegations. On the contrary, he is trying to conceal the hospital discharge letter of october 2020 from SA.
I would like to talk to a lawyer delaing with Children custody cases, to stop the husband to remove the children from Pakistan without mother’s permissions or any court orders for custody.