UV sets red

Dear All,
Happy new year to all to begin with.
I modeled and textured an asset that has multiple UV patches. I could not fit them in one patch because the textures were pixelated (using paint through in MARI) hence I used up 4 patches. I did the texturing and exported the maps. Now I’m setting up my object in UE and have found that only the first patch of UVs are white, the others are red. I have not tried to assign texture yet but will it work or do I have to start texturing again (alongside uvs)?

Another thing: The asset is a part of a tunnel in the sewers, The player needs to be able to walk inside it. Shall I set up my colliders one of the following ways:
four box colliders on each side of the place or one collider in the inside?
Thanks in advance.

Edit: for the for patches I have 4 diffuse (or base colour) and 4 normal maps. Now when I’m importing them it is a mess, I can’t get around it.