I'm not sure why you think you can only have a maximum of two characters unchained. You can absolutely unchain everyone in your party, as I did it tons of times throughout my playthrough to get everyone in their own spot before doing a surprise attack.
If you press the ~ key, it highlights characters indicating whether they're friendly, hostile, or neutral. I think, just going off of memory here so potentially wrong, that your currently controlled character is highlighted white, instead of blue like your allies. Not 100% on that, though.
