Multiple GPR targets may or may not be located.
If one GPR target is spaced beneath a second GPR target, it may be possible to record energy that is reflected back as the system approaches and passes the lower object. Otherwise, the shallower object will likely need to allow some of the ground penetrating radar signal to penetrate through and reach the deeper object. For the receiver to record a response, the signal must reflect back and make the return trip to the surface. Therefore, the shallower object must not reflect or absorb all the signal. The shallower target must allow some signal to reach the receiver of the GPR instrument.
If the shallower target reflects GPR signal very well, chances are less likely the radar signal will reach the deeper object, especially if the object is near the shallower object. Also, the limited radar signal that manages to reach the deeper object and reflect off the deeper target cannot be blocked or severely degrade by the shallower object on its path back to the receiver.
Furthermore, if the shallower object is larger and “shades” the deeper object, there is a good chance that little to no radar signal will reach the deeper object, unless it can pass through the shallower object with enough signal to make it to the deeper object and return to the GPR receiver. This is pretty iffy.
In essence, yes it is possible, but you need ideal conditions that are by no means guaranteed.