Well, this sounds a bit unfair (if it is intentional, also it assumes that all the first team is already in game when the 2nd enters) but on the other hand arquebuus is not that bad. And musketeers just die of bullets regardless whether it came from an other musketeer or arguqebus.
Both France and HRE are highly capable late/all era factions. IIRC both Sicily and Papal states have cheap pikes. Also you should be able to use the range advantage of the jan./cossak musketeers in your favour. I would be happy with a Sicilian/HRE/France/Russia line up vs the above mentioned 4 factions.
All in all, if it is intentional it is unfair but the situation is not that bad IMO.

Also I am happy that there are people who can play 4v4.