With overlapping meshes, you can bake with “exploded baking” method, or “match by name/ID” depending on the baker where Substance Painter 2 works here, for example. But with overlapping UV’s you’ll just have to bake one of the mirrored side once.
Great work, Georgian. Gonna check your tutorial for other interesting tips and tricks because I’m using Allegorithmic’s SP2 instead of Quixel.