Time Capsule & XB3 - XFinity

Currenly, we have a XB3 near my father's work computer. Connected to the XB3 is an Ethernet cable connected to a powerline adapter in a wall outlet. I then have the other powerline adapter in my room and have connected that to the input of my Time Capsulse. Now I have 4 wifi signals in my home. 2.4 & 5 from both of them. Does anyone know of the proper way to set this up? As I don't think the Time Machine function of the Time Capsule is working properly and when I access the files in the harddrive of the TC, it's extremely slow. Any assistance would be greatly appreciated.

I've attached a rudimentary sketch of how the devices appear in our condo. Unfortunately running an Ethernet cable from the XB3 is not an option, in case anyone needed to know that.