Is it possible and if it is, how to install it?
It is possible, but you will have to reinstall GRUB from within Manjaro after installing the other distribution(s). Manjaro’s GRUB has been customized and needs to be the boot loader in control.
You would normally reinstall Manjaro’s GRUB from within a
chroot environment from the live session of the Manjaro install medium. Instructions on how to do that can be found all over the forum, but basically the steps are to boot up from the install medium, open up a terminal, and then issue the following commands…
sudo su - manjaro-chroot -a grub-install --recheck --no-rs-codes update-grub exit