This feature is in beta. It is called Multi KAT. When fully released, you can control up to 3 KATs from a single phone for feedback, data collection or both. Note the sampling rate does slow down with a third KAT. (These can be mitigated with interpolation in post processing.)
Note, the human brain, as amazing as it is,  can efficiently process only a few haptic and audio inputs at one time. So we recommend enabling feeback on only one or two KATS, but not on a third KAT.  The third KAT can be used to measure other movement changes that occur because of the intervention (also called compensatory strategies) "When I increase my stride length,  my shoulder tends to dip" (or whatever).
Search also (key words): features, computer vision, mocap