HOW TO: Fix buggy lighting setup - HELP

It is my second project in Unreal and it’s becoming quite obvious that my simple lighting setup doesn’t work quite well (–> image): You see the inside of an organic apartment with light coming in through the windows. Theoretically, these surfaces should be all smooth forming one coherent interior surface (except for the floor). While there are also some things to improve on the modelling, the lighting is the main problem: I installed a direct light coming in plus a point light on the inside but the surfaces shade in various different brightnesses, even though they are the same material, also the difference between meshes is well visible (e.g. the facade vs the wall/ceiling).

What is the best way to fix this in a reasonable amount of time (10-20 hours at max but I won’t complain when it’s less if not just a few clicks) and with an low intermediate set of skills? Do I have to manually create light maps (which might be unsuitable anyway since many of the meshes are dynamic) or are there are a few simple steps by which i can fix this?

The mesh was created in 3ds Max 2017 and is mostly massive geometry, the texture was applied according to a UV map modifier in 3ds max.
The aim of the project is an architectural walkthrough.

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