How to convert a multi/sub-object material into a simple material?

hi friends.
I received an architecture project to convert it from 3DsMax to Unreal, the problem is that there are many trees in that project, and all the trees have a very extensive “multi/sub-object” material (with many textures) (Maxtree brand). I would like to turn this material into a simple material with an atlas texture for the diffuse channel, another atlas texture for the normalmap channel…etc.

I could use Render to texture from 3DsMax, but this works very slow and I saw that there are more than 70 models with more than 3 million polygons each.

In my first test, I imported the models into Unreal and reduced the size of all the textures (I also set the LODs), but I got a message about graphics card performance.

I could also enable Nanite for all trees, but these contain masked materials… so Nanite doesn’t works.

I also tried using “bake material” from Unreal but I think I did something wrong. It gave me wrong results.

Does anyone know any plugin or technique to simplify the material of the models?

Thankyou