The Whills could be something like The Hague, a place. For example, the Temple on Jeddah could be The Whills.
The Whills could be a collective noun, like the Church. The Whills could represent all those who strive to the light side of the Force.
The Whills could be a status among those who follow the Force, like a prophet or a priest or some other sort of wise person. They aren't necessarily strong in the force, but they do have an advanced understanding up the subject.
The Whills could be a group that meets, such as a council.
The Whills could be a distinctive sect of those who follow the Force.
The Whills could refer to the Force itself, in this case, the light side.
It could mean to each individual goal of the force, its whill.
The Whills could be a group of historians, those dedicated to recording events dominated by the Force.
The Whills could be a race.
It could be applied to multiples of the above, because religious groups often do things like that.
Now, which do I think are the more interesting takes on this? I like the Whills as a collective noun for those on the Light side of the force. This makes the Protector of the Whills more interesting, as they may protect places like temples, but they may just as well protect those following the light side of the Force, seeing that all is as the Force wills it.
I also like the Whills as a term for what the Force wants. In that case, the phrase, "All is as the Force whills it," becomes more interesting. Think of the whill as the same as water finding its level. The Force is forever bringing up the holes left by the dark side, but also bringing down the elevations of the Light side. The stronger that you are in the Force, the stronger that the Force works against you. The Light side understands this, and so works with the Force rather than strive against it, for striving against it is, in the long run, a losing proposition.
I like the Whills as some archaic group that left a strong legacy, one that other group picked up on and preserved, using that name as a form of legitimacy. The Whills represents a specific legacy, a touchstone, on the side of Light, but not nearly as much as I like my other two preferences.
If I was writing canon, I would make "a whill" a time/place/event where the Force is finding its level.