Many asked questions on RPCs. Here’s what I used (mainly) as a guide to RPCs inside AvatarMaster and MotionControllerBP:
&stc=1 &stc=1 &stc=1
There are of course other ways to do it, using remote roles, but I found these to be the most reliable on Steam and Oculus Network.
Also, it is also possible to reach each locally-controlled clients through the locally-controlled server, as seen in one of the Avatar Remote spawning function. Hope that it would help. 