Recently I have been having trouble with lighting in the unreal engine, as keep getting warnings that my UVs are overlapping, and the engine can’t lightmap the mesh. This took up a lot of time to fix, as most of the online help didn’t prove to be very useful. I went back into blender to try and solve the problem, and I spent a lot of time going through each mesh of the model to give it a 2nd UV channel for the lightmap, this however did not work. For the lightmap to work I needed to create a separate UV channel, keep all of the UVs separate, as well as keep them within the parameters of the texture. I then realised that the engine joins the meshes together when imported, this would mean if I had a channel for every single mesh, it would still overlap.
The solution was to simply join everything together within blender, create a 2nd UV channel for the entire model, and then automatically separate the UVs. The second UV channel was now nicely laid out and acceptable for a lightmap.