You dont need a router to make a powerline network, they allways have a star like layout keeping track of other adapters, security status, connection speed and of any connected ethernet devices.
I would be pretty confident they are point to point only i dont think they can relay inforamation even if that might improve speeds. they will not refer back to a router or switch unless they have to go thorugh it
not sure you can have redudant linkages
It would be interesting to know how the devices handle the potential for mutiple paths on some ring main layouts though perhaps its not sigfncant given the speed of transmission