This is a tough one. I am also a contractor and have invested in many properties over the past 10 years. In the Los Angeles area no less. My perspective would come from a contractors point of view.
First of all. Did they sign your construction contract? If it was outlined properly I'd suspect you'd be in the clear, but I'd still say you're in a gray area.
I see both sides of the coin because I have lived it on both sides. The investors/partners likely only want to see a nice return on investment and would probably not even batt an eye at what the cost of the rehab was if the return was met or exceeded expectations.
What is the current status with the property? Is it on the market? Pending? Sold? That'll shed some light on your the status of the situation. It sounds like the project is in the luxury market, and the price reductions in this market are prevalent. From the outside looking in it may appear you're the fall guy if the anticipated returns turned sideways.
Back to the construction. I'm not sure that most people truly understand the time and cost of a large scale project really include, and how often the timeframes and cost of goods fluctuate. This is where I feel for you if it really was a break even project for you. I've been there, you've basically worked for free for several months and now the clients/partners want more, and likely because outside parties have filled their heads up with non comparable cost comparisons regarding quality of work, materials, licensed subs or just flat out lies. I know this because I've experienced this first hand.
Again, if your construction contract was outlined correctly and signed by all parties you should be good. But that's also a lot of partners at the table that are coming for you. Their must be more to the story.
Last question. Prior to this project had you ever completed a project with these partners? Do the partners personally know one another? Are they seasoned investors?
Have they paid you the $275k in full for the construction services?
Best of luck...