Signal processing of an IVQ-3005 Radar Module
The output of an FMCW radar with linear ramp modulation (triangle or sawtooth waves) is a group of tones, one per target. The frequency of each tone gives the range of the corresponding target, and the rate at which the frequency changes gives the range rate (radial velocity). To make these measurements, you can simply add the two receiver channels together.

To measure AOA (angle of arrival), you need to compare the phase angles of the two receiver channels, as derived from the I and Q data. This processing has to be done for each target tone as well. Keep in mind that the phase "wraps" at angles greater than about &plusmn;27&deg;, according to the datasheet.

One FFT on a block of data will help you identify target tones. But I don't know what you have in mind when you apply a second FFT.