Ok so....since Reiner says he's a warrior and they have a village, I'm guessing they are like a tribe.
At the top stands the Alpha Male....who will be the strongest as well as the village Chief.
The beast Titan (who is either a new character or Dr. Jaeger) stands as the chief's head advisor or a Shawman (witch doctor).
After that would be the Warriors who would probably have ranks within itself based on strength....my guess is Reiner, Bertholdt, and Annie are either sent on their mission for being a low tier warrior, or this is a right of passage mission into advancing into a new elite tier.
So by number.
1. Chief (unknown)
2. Beast Titan (Dr. Jaeger or unknown. Also most likely only respected as the chief's advisor meaning he holds no ruling authority).
3. Warriors (probably an elite, middle, and low tier)
4. Gatherers/cooks/people who perform basic survival tasks