On server only first delete the crew i.e. driver and gunner, then delete the vehicle. If you delete the vehicle first it might cause problems.
Remember, if the vehicle is named, for example, transport1 then the driver, gunner and commander are automatically named transport1D,transport1G and transport1C. Then deleteVehicle transport1D, deleteVehicle transport1G and deleteVehicle transport1C.
You could also delete them using deleteVehicle (driver transport1), deleteVehicle (gunner transport1) and deleteVehicle (commander transport1).