Mesh merging light issues

Hi everyone,
I’m trying to merge multiple meshes aumatically but it seems that there is a problem with the lightning…https://jsfiddle.net/f9zeymvj/14/
I work on an other platform and there is what i can see inside of the merged mesh:


Is there a way to completely merge meshes ? I know I can try to work with the vertices and the faces but I quite can’t figure how to do it…
Thanks