You're welcome! I'm happy to help! Okay! That sounds good. Correct me if I'm wrong, but I think that means you want them? I can remove them if I've misinterpreted, and I'll include the reasons.
Honeymooners - Post Av1 Te'ijalahad; (very) strong language & brief, non-explicit sexual references (it's not between them - Galahad studies up his mythology and learns some things he'd rather not).
Basic Survival Skills - Early Av1 Rhen & Lars fic, platonic. Strong language, animal death, and mild gore (it's about their failed attempt to skin an ox).
Sun's Up Gun's Up - Grand Theft Auto AU, focused on Rhen, Lars, and John, but including characters from Av1/2/3/4. Drugs, violence, suggestive, lots of (very) strong language.
two sides of one coin - platonic Rhen & Lars, retelling of Aveyond 1 (removes all other party members but John). Strong language, I don't remember if there's anything else earning its T-rating, or just that!
And the te'ijalahad fic is hosted here - Night Falls. Canon divergent Av3 fic, that occurs somewhere along the course of the journey. I've gotten wistful about its unfinished status every time I've thought about it for the past eight years, so I'm giving it a big disclaimer for that.
Whooops! Meant to reply to this and life got ahead of me - I was going to go ahead and go compile a big list, but instead of put it off further I'll just give you what I have so far.
Waiting by Marabelle is a blast-from-the-past Av3 Te'ijalahad fanfic I read the first time I was on the forums, from 2009. I know this isn't a rec list, but it'd feel remiss not to say this is my favorite te'ijalahad fic of all time. Also Te'ijalahad and by Marabelle are If At First You Don't Succeed... (a post Aveyond 1 oneshot). She wrote one more fic, but it was multichap and unfinished since 2010?, so I hesitate to link it.
Postmortem is a reflective, Av1-Av3 Galahad-centric, te'ijalahad fic by Rena.
While I'm going through and listing late 2000s/early 2010s fic; I was skimming through fic I read in elementary school by an author who did a lot of Rhen/Lars. On Fanfiction, they posted:
Love Potion Dilemma
How Long (post game; hermit ending)
It Isn't Right (platonic)
Stuck (mostly friends)
Time for more recent fics! These are all on AO3, since that's where I've been most recently. I don't know how master you want this masterlist; a couple of these are decidedly rated Teen and Up (for things ranging from violence to suggestive content/references to strong language to mild gore), so it might be best not to link them.
Aislday Adventures was written for the Winter Exchange last year; it's AV3 Te'ijalahad.
What Was Lost is a Te'ijal and Gyendal centric fic!
I'll go ahead and link my own fic (w/ the Amaranth link); Now We're Two of A Crime, which is a Boyle & Myst friendship fic.
The Annual Pendragon-Johnson Hannuchristmas Double Holiday Banquet and Bash XXXIV is Teen rated, but not in a way that makes me question its appropriateness linking. It's a Mel/Stella/Lydia fic with a lot of background relationships and interactions, including John as Mel's dad, which I am super super charmed by. It's by Ishti, who also wrote the last fic I'll link to right now!
Rhenegade! This is my favorite Aveyond fic and maaay have become my headcanon for Aveyond 1 as a game. Don't get me wrong, I love the original, but the way this fic tackles the narrative and elaborates on everyone's characters is phenomenal. It reads partly like a fic, partly like an original fantasy novel. Main relationships are Rhen & Pirate John, Rhen & Peter, Lars & Talia, and Lars/Dameon, but a good deal of others get some spotlight. It's about 2/3 finished but is still a work in progress!
I intend to get back into reading more fic soon/eventually and can continue to send links as I do! But this is hopefully a good starting place.
Oh boy I know a lot of fics, I can try to give some! Do they all have to be posted on Aveyond Studios? I know some by their Archive of Our Own links instead/am not sure/know they don't have copies here.