Hi, and welcome to TONMO. com
I've been trying to find out more about keeping more than one octopus in a tank all year long. So far this is what I've been advised:
You can keep more than one octopus in a tank
IF you have a very large tank
IF you have more dens than octopuses
IF you feed the octopuses very well
IF they are always the same size
Otherwise, they may eat each other.
Joubini is a small octopus (also known as the Small-egg Caribbean Pygmy Octopus). It even lives off of our Texas coast. I can't remember any TONMO member ever keeping one. Don't know where you might get one, but someone might offer it.
Nancy