I think Paragon might be easier on Oversoul, because his physical attacks missed me a lot for some reason.
As for Trema, his physical attack can inflict stop, so something to guard against that is needed, such as high luck. He only has 999 MP so drain with things such as Soul Springs or Mana Springs. That way, he can't use Flare, Demi or Ultima. He can still use Meteor though, but only twice in the battle. Also, using a chocobo wing to get a speed advantage is good too. I think most of the strategy for beating Trema has already been said by other people.
If it still doesn't work, leveling up could help.
Oh and an interesting thing is, after you beat Trema (this might be a spoiler)
(SPOILER)You can go back to fight Paragon