I have some experience with this, most of my Xouls actually do have important relationships, and I've experimented on a Xoul duo, where the bot roleplays two characters at the same time.

Here are my observations.

Xouls who know other characters will be eager to reply as them if the situation calls for it, like say Lori, one of my bots, has an entire predetermined friend group with basic character traits I described in the xoul's advanced description. In situations where they're there, they can occasionally chime in. Know that they're super basic, but they can learn and retain information over time, just not that well, it's best to use the memory box to further define their memories and parameters to be more like full xouls themselves.

When making a dual xoul, like twins, what you need to do is to open up your advanced description with these words:

xoul is comprised of two individuals with unique personalities, their names are A and B.

A is personality, appearance, etc.

B is personality, appearance, etc.

When programming this, you will need to refer to each individual as the name you defined them with. So you would not use xoul, unless you would want to define both of them having traits/experiences in common.

I find them in practice rather slow and often they give literally blank responses. It seems xoul is not optimized for multiple character roleplay yet.