see here: Best NATRON Tutorial
Use several “merge nodes”, each one has an “A” and “B” pipe.
Merging images — Natron 2.5.0 documentation
to move the “Center Point” just “CTRL+click” onto the gizmo to move.
hit “S” to set the main resolution of your work, for safety I often start with a “Solid node” to keep the size.
see here: Project setup — Natron 2.5.0 documentation