But I think I already encountered him. Is that the little lvl 5 guy that asks to not kill him for his XP?
No, that's Good Glenrick. He uses a Crusader sprite, but he's not in any way involved in unlocking the Crusader.
Both the Earthmother and Goblin are unlocked in the Southern region, and will be found randomly in a subdungeon there. You must have already unlocked Tikki Tooki before the Earthmother will appear. Play in the Southern Swamp, Hexx Ruins, Ick Swamp, or Slime Pit. The Earthmother is easy to unlock if you find her subdungeon, just make your way to her altar. The goblin will require you to pay him money up front, at which point the race will be unlocked when you retire from the dungeon, so bring gold as a preparation.