Option (4) is safer in the long run because it prevents boot loaders overwriting each other.
Also, dual-booting and accessing the same data in /home IS ONLY SAFE IF YOU DO A FULL SHUTDOWN ON EACH BOOT OF THE OTHER SYSTEM. No hibernate, because hibernate does not unmount file systems.
Option (4) is safer in the long run because it prevents boot loaders overwriting each other.
Also, dual-booting and accessing the same data in /home IS ONLY SAFE IF YOU DO A FULL SHUTDOWN ON EACH BOOT OF THE OTHER SYSTEM. No hibernate, because hibernate does not unmount file systems.
If you want to keep both running, a VM (for example running in GNOME Boxes) is both safer and much more convenient.