... > to know if there is a way for all three of them to share the same disk > space (I mean to share a partition between all of them). ...
We do this all the time. The easiest candidates for sharing are /opt and /usr. By default, they get put into the root filesystem, so you need to give them their own partitions at installtion time. You might have three full 3390 volumes: root, /usr, and /opt. (You will have to decide how large to make these. If you have VM, certainly you can make them smaller.) Once you have installed with /opt and /usr being not part of the root, you can COPY the root device (using something like DDR) to another minidisk (or full pack) for each of the sharing images. Each of the sharing Linux images will then have the same idea about the content of /usr and /opt as the owning Linux image will have. But each of the sharing Linux images will have its own root device. You then MODIFY /etc/fstab on each of the sharing Linux instances, as well as other things (to change their hostname, IP addr, so forth) so that /usr and /opt are read-only. I recommend making them read-only to all, including the "owner", the owning Linux image. Voi-la.
