Superimpose multiple MRIs

I have a problem because I can’t superimpose multiple MRIs.
I’m trying to reconstruct a 3D model of my brain but I have a problem.
I have selected 3 scans with the best resolution but I have to merge them because, for each plane, there is a scan with a higher resolution.
The optimal scan for the frontal plane is the first, for the horizontal plane the second and for the lateral plane the third.

How do I make the program use the scan I prefer only for a specific plan and not for all three?

This question comes up from time to time. These links should give you some ideas: