Goblin girl hearts are based on tribe size, or maybe how many kids each one has.The Goblins population I beleive is connected to overall population(?)
Caleah I beleive is stuck at 4 hearts right now & Oksana is stuck at 3. Dunno why.
Caleah can get to 5 hearts, 99% sure you need to do at least two picnic dates to get there. Unsure about Oksana.