For an additional bit of reading I’d also recommend taking a look at the documents put together for the Triglavian Compendium assembled by ARC. Parts of it are in-character from a (kinda sorta) EDENCOM-aligned group (its a long story best told by them) so bare that in mind if you’re hoping to make content from the Trigs perspective. Its an irrefutably detailed and well constructed piece though and I recommend giving it a look for more detailed information and snapshots on the Trigs.
KINDA IMPORTANT: Their webhost that their content was originally posted on seems like its down but you can still access the documents by copying the links and plugging them into the Wayback Machine here.
Theres a lot of other documentation assembled from other sources that I’m sure I’m forgetting, and as far as I know there hasn’t been a single source to compile all the information and context on the Trig civilization that’s surfaced from the newest Faction Warfare arc. If anyone from any of the militias has anything saved, I’d encourage that they post it here. I’m far more familiar with the Placid arc than Tannor, as that was were the Triglavian presence was strongest and most active outside of Pochven.