Don't you want to go the easy way, installing the distribution on each
partition (sda2, sda3 and sda4), one by one? After all, an installation takes
something like 20 minutes. And you do not have to stay idle (you can use the
live system during the install).
I assume you have already a separated /home partition that should be common
to all systems. So, if you follow the way I propose, do not forget to specify
that with at the "custom partitioning" step. And double check that you did
not ask for the erasure of that partition! You also want to double check that
you properly spelled the (same) user name and the (same) password every time.
In fact, for security, I would personally not specify the /home partition
(everything in /) and, after the installations, edit the /etc/fstab files of
all three systems.
