Combining two separate radar signals? I have two small radar sensors that use 25 MHz. From each sensor I get the sent signal and received signal (Doppler effect). I know that I can use the FFT, use a window, or FIR filter, take the inverse, and get the frequency within that window. Thus I can analyze the signals separately. I'll have two plots. The radars can be positioned in 3D space at different points, but they can be pointed at the same point in space or at different points.

Is there any way to combine the two signals to analyze motion? For example if one sensor is pointed at the cheek and the second sensor is pointed at the chin, can I somehow average the signals to get one signal that represents the observation of the cheek and the chin? Can I average the two separate plots together?

Or say we had a spinning top. One sensor is on the right and another on the left. If the top leans right the sensor on the right gets less of a time delay and the sensor on the left gets a longer time delay for the received signal. Thus using the information from both I can tell at what angle the top is spinning hypothetically because speed is distance over time. 

Any help, math equations or references would be appreciated.
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