I'm sure that 4 clerics can finish the game with Craft and scribescroll. The only party that really can't get through the game is a party of 4 knights. Everthing else, can.
My point is if you want to finish the game with 4 clerics, don't surrender, is totally possible. (I'm not even saying that any party can with reloading a lot, I'm saying that any non 4 knight party can Ironman the game)
Again if you want tips on how to beat the Green dragon with 4 clerics, I can, if you want to use them. Though I would need to know feats and spells. Having Protection from acid is very important, but even without it, I think it's totally feasible at level 8. You can send me the save file if you want, I would find fun trying to find optimal tactics on how to beat the dragon with whatever you got there.