I tried to use similar gens to your team.
Pothinus whitout items in the swordman.
Pedius whit geography item(gallic war) in the javalinier.
Labienus(4 calv stars) in the heavy calvary, whit +3 range artifact on him.
Move your inf and archer gen whit other 2 troops to the south, focus killing the enemy gen whit your archer and take the allied city when possible.
Move Labienus, your calv gen, and the rest of your troops to take the city in the north, then support your allies in the middle city and take it when is open.
To hold your starting city just make a ligh infantry and a slinger.
banner pngUse the city you took in the north and the city in the south to replenish your troops, then wipe out the dangerous enemy troops in the middle, after it is safe go for the last city.
For the population mission build scouts, they are cheap and give 2 population
You should be rich but if you need money sell your cities upgrades.
For tech, research the upgrade that allows to recover city defence whit enemy units around.
alright thanks, I still have some questions, namely what do you mean with go south, the allied city in the middle or the bottom one?