If it is one root with two 4 prong tops... don't think most would agree with calling it a 8 prong.
I have found single roots with 3 tops before and have seen others that had as many as 4 tops off one root.
My single root that had 3 tops, had 3 - 3 prong tops.
I did not call it a 9 prong though
To me - before you can call it a X-Prong it needs to have 1 stem, and X number of branches off that 1 stem.
I have a friend whos dad found one that had 1 stem that went up to a 4 prong top, then where the berry stem usually is a stem continued on up from that to a 3 prong top, then it had a berry pod on top of that.
That is sort of a double decker top and I think in that case it could be called a 7 prong.
Not sure if there is any official ruling on this subject though.
Either way - nice root you have there and nice top(s) too.
Congrats !
TNhunter