
TheFinish |

Thematically, they should stack. But the wording is ambiguous, so I'm not entirely sure.
Titan Wrestler is pretty clear: you can affect stuff up to two (or three) sizes larger than you. Cool.
Larger than Life says that as long as you're in Heavy Armor, you are treated as one size larger for determining stuff.
You have both feats, you go to Grapple some dude. It becomes an order of operations thing. Do we do LtL first, so I count as Large, and Titan Wrestler lets me grapple Huge and Gargantuan? Or we do Titan Wrestler first, so I'm Medium, and I can grapple Large and Huge, therefore making the first half of LtL useless?
I personally think they should stack, as said earlier, but I don't think they do as written. At least, it's not a given.

Teridax |

For reference, the text for Larger than Life is this:
When you are clad in the heaviest of armors, you have an outsize presence. Though you don’t get any larger, you are treated as one size larger for the purposes of affecting other creatures with actions like Disarm, Grapple, Reposition, Shove, and Trip while wearing heavy armor; similarly, you are treated as one size larger for the purposes of creatures affecting you with those same actions, as well as Swallow Whole and similar actions, while wearing heavy armor.
So effectively, you're treated as one size larger than your actual size when using Athletics maneuvers against creatures. The text for Titan Wrestler is as follows:
You can attempt to Disarm, Grapple, Reposition, Shove, or Trip creatures up to two sizes larger than you, or up to three sizes larger than you if you’re legendary in Athletics.
So you can use Athletics maneuvers against creatures up to two sizes larger than you... which could refer either to your actual size, or the size you're treated as thanks to Larger than Life. The wording is therefore ambiguous, and given how weak the feat looks outside of edge cases involving Hampering Sweeps and abuse of size increases against monsters with size-based abilities like Swallow Whole, I'd probably rule in favor of both stacking right now. I also personally hate the feat and don't think it should exist in its current implementation, but that's another matter.

Teridax |

I kinda wish the feat was more extreme, or had a buffed upgrade later. Something that gave you a full phantom size category. It'd especially help with your intercepts needing you to be adjacent to allies.
I feel this could've been an opportunity for a "skill feat+" class feat. Titan Wrestler is already the feat you get to use Athletics against larger creatures, and that plus a component that protected you better against Athletics maneuvers against you, as well as other abilities with a size component, would likely be enough for a 1st-level class feat. It would also, importantly, eliminate the current ambiguity around two similar effects stacking.
As for being able to intercept more easily, having this aura that lets you Intercept Strikes and protect adjacent allies from farther away could be really cool, as beyond Intercept Strikes there are a lot of guardian feats that require you to be adjacent to allies. I'd support some version of that, provided it was phrased clearly enough.