://imgur/Fz461Cc
How am i supposed to deal with this overlapping?
rebuild the meshes so they do not overlap anymore.
That’s called z fighting. As Killspree mentioned, you will have to rebuild your mesh so that those parts are not overlapping anymore 
If you move up a mesh at z+/- 0.01, or rotate similar(x+y), it stops fighting.
If the static mesh overlaps with another, the parts that are not shown are they still rendered? or cause any other performance issues? For example if I copy a rock static mesh and overlap them to make a cliff wall