Q1. Do you always have the lowest stability if you have 0?
You do always have Least Stability if you have stability <0. The rules do not distinguish between any values lower than 0 for determining Least Stability. Each player with less stability than 0 ties for Least Stability (in a 5 or 6 player game, perhaps joined by those with stability 0â‰¥ as well).
Q2. If one player has -3 stability and you have 0, do you both have the least stability?
A1. In a 5 or 6 player game, probably. In a 5 or 6 player game, the player with -3 stability is certainly Least Stability, because that is less than 0 and "in revolt." The player with 0 stability will also have Least Stability unless a third (or fourth, or fifth) player is also in revolt with <0 stability.
In a 2-4 player game, the player with -3 is certainly Least Stability. The player with 0 stability is not tied with <0 stability, so does not have Least Stability.