This battle has alot going on, as you'd expect. Your forces can handle themselves pretty well so long as you give them a hand here and there. Except Xiahou Ba, who gets wrecked almost immediately after the cutscene. After the cutscene more enemies appear, some of which on cliffs throwing boulders down on you from above. They're annoying, but you can ignore them outright cuz they never move from their position. If you kept the four main bases protected for most the battle then Zhuge Liang will have a single officer appear in each attempting to take it, if not then once one of them falls he'll spawn all 4 officers in a single base to make a charge on the main camp. After this Sima Yi will have a plan to get Wei Yan to defect, which he will then do if you approach him. However he defects back to Shu when he gets near Liu Bei, and powers up.
The targets are to defeat Guan Ping and Yue Ying in 10 minutes, protect the 4 bases for 15 minutes, and keep 7 or more officers alive. Guan Ping and Yue Ying can be dealt with after you build up the renbu for it, but Yue Ying has juggernauts so beware of that. The 4 bases are the hardest to keep safe and honestly involves a bit of luck so just stick near them and help immediately when the enemy officers appear. Keeping your allies alive is simply just doing the stage well enough. You yourself count as 1 and if Cao Cao dies you lose so you already have 2 kept alive by default.