The issue is your lightmap UV’s, you need your second UV channel to be flattened out and fit into the 0-1 UV space: Unwrapping UVs for Lightmaps | Unreal Engine Documentation
In your case for something like walls, I would do an automatic flatten and then if you can’t get enough detail in your lightmap at a high resolution like 1024x1024 then split the mesh into separate objects so that it can use more lightmaps. Try not to separate anything on a flat surface, so for a wall you would want to split on the corners and not the middle of the wall.
For things like floors/ceiling just do a planar mapping.