I’m not sure why you would really need UV channel 2 with this method.
If each mesh has its own texture you can setup each of the the four meshes to be in UV1 (3Ds Max and other programs, this will be UV 0 in UE4). They can overlap all they like and it will not matter since you’re using Multi-Sub-Object material and these individual meshes are given their own material ID.
So at this point you really only need a single UV for all four meshes for your textures.
Next you’ll want to setup a Lightmap UV for the second UV channel (3Ds Max and other programs, this will be UV 1 in UE4). In this UV it is imperative that none of the faces overlap for all four meshes. This is where you’re lighting information will be baked in UE4.
When you import your mesh into UE4 and open it in the Static Mesh editor, you’ll notice that you have four Material slots, and two UVs. If you enable the UV button in the toolbar so you can see your UV you should see a mess of UVs overlapping for UV0 (UV1 in modeling programs). If you use the drop down you can select UV 1 (UV2 in modeling programs) to view your lightmap layout where there should be no overlapping faces.
In the details panel in the SM editor double check the Settings tab and make sure that Lightmap Coordinate Index is set to 1. This will assign your UV1 to be the lightmap.
I hope this helps.