Start with Gold Armored Rhino near the battlefield full of corpses, he's tough but easiest of the four. Good to learn his charge patterns since other bosses use similar moves.

Head to Cloudtreading Deer next, wait for his jumping attack then get some hits in before backing off. Interesting tip the deer sometimes gets stuck on terrain which gives free hits but dont rely on it.

After that find Feng-Tail General, watch out for his spinning attacks they can catch you off guard if youre too aggressive.

Last one is Emerald-Armed Mantis, appears near the golden tree in middle of the water inside Zhu Bajie, definitely the hardest of the bunch so make sure youre prepared. Maybe worth knowing you can actually parry most of his attacks but timing is super strict. Best to get these done in order since some armor effects work together and dropping any might lock you out of good combinations, plus the mantis wont show up till you beat the general anyway.

Good idea to explore the areas between fights cause there's useful stuff hidden around that helps with later bosses.