I am playing on easy and it seems too take forever too level too 25 for end battle is the catacombs the easy way or robbing missions.

You don't need to level to 25 for the end game when playing on easy. There's only one difficult fight in the end game, and that's the first one, so you'll immediately know if you can finish. You may want to bring some bombs though, just in case.

my characters are only level 11 and 10 so they only have about 100 hit points.

To level up in Easy, doing the catacombs is the fastest way I think (has been a while since I did a playthrough). Anyway I think that finishing the catacombs you should be around level 20 at least, enough to finish the game at that difficulty level!

Agreed, catacombs give faster leveling than robbing. (I did manage to finish Easy with my characters at level 6 for the end game, but that wasn't so "easy.")