I'm in a cohabitating Vee also. One thing I've personally observed, for my own experience, is that privacy can be an important issue. I need to be able to "retreat into my cave" sometimes.
My Vee is an MFM configuration, with the lady of the household as the "hinge." Us two men (who are platonic friends with each other) have separate bedrooms, and my bedroom has an attached bathroom. I can't tell you how valuable that set-up is for me. Just knowing I don't have to "emerge" unless/until I'm ready, makes me feel more inclined to emerge more often. But, then, I've always had an introverted side.
I think it's a challenge anytime multiple people share a living space, let alone when it's also a poly sitch. Just think about a regular monogamous couple, almost everyone has problems learning how to live together. So you really have to learn a lot by trial and error. Each individual person is so different and unique, they all have their "tips and tricks."
Our first few years together (as a Vee) were rough. We had to have separate domiciles for awhile. Things just gradually smoothed out over time. Now we have a comfortable, boring dynamic with each other, and we love it.
We first got together (as a Vee) in 2006. It took til 2009 or 2010 for things to really start smoothing out.
Another challenge is I have had a short fuse and big mood swings in the past. For some reason I've finally calmed down, perhaps because I'm finally taking the "winning combo of meds." But who knows.