My advice is:
0. Realistically assess how much money is actually involved right now and what the odds are that it is significantly more at some future time.
1. Think about what you really want and then act upon it.
2. Realize that a nasty legal fight is going to suck up your energy and time.
[IANAL]
It does not matter what a typical settlement is. It matters what happens in this particular context, with the particular people involved, at this particular time.
If you have a realistic current valuation of 1/3 ownership that discounts future value for time and risk, one option is to negotiate a buyout toward that value. This allows you to walk away.
If the realistic current value is zero or close to it (i.e. significantly less than a few or one hundred thousand dollars), maybe it is worth sitting tight beyond minimal actions that clarify your claim and seeing what happens over the next few years. If the stake becomes significantly more valuable, then it might be worth a nasty legal fight. It probably won't.
Essentially, the big decisions are
1. Whether to play long term or short term.
2. Whether destruction or success is the preferred outcome.
3. Whether to look at the pie as finite size (in thirds) or potentially huge -- a tenth of a unicorn is a lot of meat.
I had a somewhat parallel experience many years ago. One day, in the midst of it, I decided what kind of person I wanted to be. In that sense it worked out well.
Good luck.