I believe when a family member is in trouble, you circle the wagons and protect the family. That's not a universally held value, and I expect some people will disagree.
TLDR: It's an ugly situation. But family first, the legal battle is likely to be a money-loser, and the emotional cost will hurt even more.
Condos are cheap. Family is priceless.
Tearing apart a family over a simple money matter isn't even stupid.
The family should resist the urge to use the financial situation to teach Jane a "life lesson". Of course there are fears; but fears over not getting a windfall seem silly. I certainly know the rationalizations: being accommodating to the poorest family member could hypothetically be a 'slippery slide' to more dependency. The tragedy of the commons. Atlas Shrugged and the American "achieve for oneself" ideal. But realistically, turning it into a battle will not give her any needed education. The siblings are much better off shaping the situation so Jane has new experience of success in a relatively safe and sheltered environment. Learning happens there.
Besides, maybe stability, trust, and family love is the real wealth.
Treat the condo like a trust to protect/benefit the family
So that when a family member really needs it, they're assured a place to live and won't have to live in some deplorable situation, in a homeless camp or in an abusive relationship they hate simply to have a roof over their head.
In fact, if they dislike Jane, they'd rather NOT have Jane move in with them, so maybe avoiding that is worth temporarily delaying an unexpected and unneeded windfall.
So rent it to Jane, enjoy the revenue stream even if sometimes intermittent. When she moves to better digs, rent it out for a revenue stream for all of you including Jane.
Or let Jane buy them out. Carry paper.
Since she doesn't have the cash, carry paper. Then, be a chill banker since this is family. This works better for the "lenders" - rather than get a big wad of cash (which people tend to "blow" with nothing to show for it later), they get an ongoing income stream, and their first taste of the real estate biz. Hopefully not their last.
Meanwhile Jane is on the path to home ownership, which can be a great life teacher and motivator. It's quite possible she'll get excited about this and want to accelerate mortgage payments simply so she can say "Mine!" That's a great life lesson.
The direct answer
OP asked why the big detour, why didn't I answer the question directly like BrianDHall did. I didn't see any percentage in a frontal approach because I don't think it'll work.
Judges will take the view from 30,000 feet; i.e. she's going to be looking at all of the above (which is why I put it first). Judges really don't want to be the "heavy" or solve wobblers like this. Like the original Solomon, she'll seek to avoid adjudicating it. She'll probably order you back to settlement talks (with court approval this time) and an admonishment not to make any homeowners homeless and what is wrong with you people, honestly. After all, Jane is only 17% shy of this matter adjudicating itself. She will be very reluctant to make someone homeless over 17%, especially when the "injured" parties are not injured at all.
There are so many other ways to work this out; the judge isn't going to force anything until she's seen good reasons why all of them failed.
She doesn't want to decide it because the law here is a morass, there isn't a stack of favorable case law to make her decision clear. Evicting an owner merely because they're 17% shy of total control? How do the rent-control laws in the state apply here? Does being an owner bypass the normal eviction laws? Is Jane both protected by, and liable for, landlord mistakes? Jane is destitute and probably under-represented, which obliges the court to protect her somewhat. These are fertile grounds for an appeal, and the judge knows Jane can't afford one. So she'll err on the side of making the other two file the appeal!
Costs will sneak up on the two. Your lawyer says "We can get this done for $5000" and then Jane goes to legal aid and puts up a pretty good fight, and it ends up being $12,000 by the time you get spanked back into settlement by the judge. "Only $4000 more and done" -- etc. etc like an apple on a stick. And if Jane can't afford legal, you have a pro-se litigant, which can self-destruct, sure. Or can be smart and determined, with nothing better to do all day but drive up your costs. I've gone up against those - no fun.
Even worse, the judge is all onboard with breaking the two with legal costs. She considers them morally in the wrong, and wants to illustrate to them that the right thing is often the cheapest thing. What would Solomon do? And believe me, she knows exactly what the two are paying, because she was an attorney. I think this will be a total cash loss for the two.
As the Ferengi say, "there's no profit in it".
And one more thing.
Emotional energy isn't free
Obviously, this whole situation is a bottomless emotional pit-of-hell for all parties. This itself is extremely damaging to your success.
I know of a small business that was doing rather well. It was run by a detail-oriented, smart, and a bit obsessive guy - a perfect alchemy for success in that business. However, a networking provider managed to screw up a configuration for his website, in a really persistent way that affected his website for a year. Now, instead of "just get another website", he got another website called
<provider>RippedMeOff.com and went full-on Don Quixote attacking this faceless corporation in a series of lawsuits and social-media campaigns. The corporation barely noticed, but it tied him up good and plenty. He failed to notice that his business just withered, and he ended up losing a half million dollars in revenue. All over a $12 web site.
Never mind the court costs. Like the failed businessman, the two should be mindful of how such a battle will impact their business opportunities, social opportunities, job performance, sense of peace and prosperity, overall happiness, and health.
The two need to ruthlessly guard those things, and not allow some diddly business with Jane to threaten them in any way whatsoever. That is a selfish view, in the best sense of the word.