Rex X Pyra X Mythra: What is the relationship?

Hey. I wanted to discuss this, but I was afraid to post it on social media. Anyway, all the way through Xenoblade 2, I never quite understood Rex, Pyra, and Mythra's relationship. Is it love? Friendship? Is it polygamous or are Pyra and Mythra seen as one person?
If we are talking ships, I think Rex X Nia would work better, but maybe I shouldn't get a shipping war started.
What do you guys think? I'm sorry if it's a really stupid question.

Pyra and Mythra are definitely seen as one person. Although most people prefer one personality over the other. I would say Pyra/Mythra is similar to Fiora (XB1), and Nia is similar to Melia (XB1). I say this because Pyra/Mythra is Rex's main love interest but Nia really loves Rex and Rex kind of just doesn't notice or pay attention.

also yes, a lot of fans prefer Nia with Rex