About FFX-2
Interesting cause you have Trema - Vegnagun, but there are also Paragon, Strongest Shinra and Numerus.

I'd say Trema, Strongest Shinra and Numerus would definitely beat Vegnagun. I think it's funny how Trema simply jumps in front of Paragon and kills him. I somehow doubt Paragon could beat Vegnagun - we don't even know whether Sin or Vegnagun is stronger, do we (although it certainly looks like Sin would win)?

So I think Trema would easily kill Vegnagun but would lose to Numerus and Strongest Shinra. Paragon would lose to Numerus, Trema and Vegnagun. Strongest Shinra, though, is probably even stronger than Numerus. Braska's Final Aeon... would probably lose to Trema, Shinra and Numerus. Maybe the three of them put together could even stand a chance against Sin in his whole power.

About FFVIII
Ultimecia seems to have tried to tame Omega Weapon, but couldn't and simply locked him away. Triggering the bell opens the cage. Anyway, Ultimecia IMO couldn't defeat Omega Weapon.

About FFVII
Sephiroth would kill those WEAPONs. The ShinRa managed to defeat Sapphire Weapon, so why shouldn't Sephiroth be capable of killing 'em?

About FFX
"JUDGEMENT DAY" and Braska's Final Aeon is dead. I don't believe he'd stand a chance against Penance. Nemesis... maybe, but I doubt it.

About FFXIII
In spoilers, of courseI doubt either Vercingetorix or a Long Gui could stand a chance against Orphan. Either is very strong, but Orphan is an incredibly powerful Fal'Cie.