@notTheCat @linux I haven't tried this but I think a shared boot partition and one installation of grub (I suppose the version you like the most, if you have a preference). You might even want to install grub from neither and do it by hand, just to make sure they won't mess it up. About shared home: not sure. It will work - I just don't know how many little oddities there will be.
EFI partition can be deleted and re-created.
@KarunaX @mozz and it will. The UN seems to be a venue for white supremacists to always get what they want, these days.