let me break up 6vs6 class distribution for you guys.
First of all most of the team that you guys are gonna encounter in the league will have this class lineup of 2 scouts, 2 soldiers, 1 demo and 1 medic. So it is very advisable to go with the same format.
Scouts should be the most versatile players, preferably they should know how to play sniper, heavy and engineer. Soldiers and demo should be very dedicated to their class.
Pyros have to be used very tactfully otherwise just using them is a total waste. Spies are a class which are hardly used but can very effective. But if you guys are gonna run a dedicated spy in the whole match then other team will regularly spy check and it would be waste again. Heavy imo is only useful in dustbowl or defending last checkpoint.
EDIT: I forgot sharekhan is on your team .... please consult him as he will be able help you out better than me.