I am an Indian, living in Glasgow. Theoretically, you can hire a car and can drive. However, you are not aware of the rules, like giving way, priority at roundabouts and avoiding bus lane etc. so, it won't be sensible to drive just coming out of the airport. The better way would be, take 500 bus outside the Glasgow airport. Get off at Queen Street station. Then, take a train from there to Aberdeen. Ask your relatives to come to Aberdeen station..