You might find on the wiki some references to networking two tinyGv8s together, it is not clear how well it works.
The likely best answer for you is to study up on tinyG2, as it is rapidly improving and in-use by many. It is still Edgy but if you need >3 independent axis control, likely your best bet.
tinyGv8 has only enough compute horsepower to deal with 4 axis channels.
Networked tinyGs was intended to share a >3 axis Gcode stream across two compute engines, Folks making custom machines (and compiles) made it work, but G2 is likely the easier to go forward path and lower cost to boot, if that matters.
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