GPA based quarry

GPA executed to a concubine by a man in abudabi. he have wife 3 daughters and son.wife filed maintenance case against him and for charge of the property. this concubine brought 3 other GPA in different propertss later also. meanwhile executent died. some of the purchase filed case for specific performance suit against wife and children.my question GPA of a foreign country without registering it is valid? another can a Pearson can take number of GPAs in her name? third what is the procedure of genuine verification of that GPA executed in foreign countries?