Or more simply, leave space on the initial install, both use anaconda that is easy to step up hard drives with, just select custom, if you don't know what your doing stick simply to a Swap partition (you will only need one for both partitions so don't bother creating a secondary one for the second OS) that is either twice or three times the size of your RAM, Then create one partition with a label of /. Remember to leave space for the other OS. You could also create a shared partition between the two and give it an uncommon name, for example /osshare. remember to leave space then install. Then get the next distribution, install, use remaining space or go custom and just create a single / partition.
If you did create a shared partition you will need to add it to the /etc/fstab of the alternative distributions OS to the one that installed/created it. This is the cleaner and safer way to preform this task.