This is the file where dialogue, quests, and claims for the eastern Thirr should be merged. Do not edit this file without also loading TR_Mainland.esp, and do not merge other esps into it without also loading TR_Mainland.esm! (see editing guidelines)
As we have no idea what the version which Rats has checked out looks like, no work on the file can currently be done.
What generally needs to be done is finish the Aanthirin visual overhaul, NPC Gol Mok and replace the ship in the harbour with a boat, replace the interior of the Velothi tower that leads to a Stronghold ruin with the actually intended one, and widen Veloth's Path under the parameters that Indoril-Thirr does.