Personally i like this tree civs but as you can see they are not used at all.
Italians: I think they can focus this civ more to archers, taking out hussar upgrades and goving them a bonus in wich archer get plus 1 attack with any relic they take till 3 or 4(not affecting genoese crossbow) (wich have sense to me as italie has been a religious center since a long time ago, so giving them a little religious- military power wont be that crazy, i think ).
Turks, as their main power and identity is gold and they are kind of weak in late game as thei dont have any trash I think there are two options, first you can give a little bit more of power to their hussars making the sipahi affect them to. Or you can make their gold mines last longer and reinforce their late game as they would have gold access trough a longer period of time
Portuguese, I think this last one makes less sence and can be kinda crazy but i imagined a way to give them a little bit more of power is to give them a khmer farm bonus but with gold and i personally dont think this will be broken as gold will finish earlier for them so they will lose this advantage eventually (not as khmer farms that can last forever in the game ( i dont think khmer is broken now)). Or I have two more options that can be less crazy, firstly you can give them hussar reinforcing a little bit their power against skirms and late game or you can give feitoria littlebit more of poer making them more rentable as the game goes on.
This is a personal opinion and ideas that i think can give the game more balance than it has now(i would love if you agree with me you can support my idea and if not please leave your comment below respectfully)