Combining two separate radar signals?
Yes, there is a way to combine radar sensor data.  There are instances where you can correlate the two signals with each other, but it depends on what you are trying to do.  A couple of points about your examples:

Chin/cheek.  At 25 MHz, any reasonable aperture (antenna) will likely have a large enough beamwidth that both sensors would see the same thing: both cheek and chin.  That said, you may see a Doppler shift from both objects.

Top.  Conjugate one of them, provided that all other parameters are exactly the same.  That said, one sensor is already measuring the exact event that you describe.  If you need higher SNR, there are other things you can do.  

And don't forget that each radar can pollute each other's data