Boy, what a painful experience this is for you. My condolences.
I am very fortunate to have stairs that go straight down to my basement shop. There was only once that I built a project so large as to concern me about it removal from said shop. I took measurement after measurement double checking as much as possible.
What I'm thinking is that either your project has to get some creative modifications or some parts rebuilt.
If changing the project in any way isn't possible, then some changes to the house will have to be done, assuming you don't want to leave the table in the basement.
To be honest, from my POV, dining tables ought to have removeable portions just to make it easier or even possible to get in and out of a room. I built a plain old Shaker style table, about as ordinary in design as can be, but made sure the legs were removeable. Otherwise it may still live in my basement. Or be unable to pass the average doorway.
I've toured through the new houses of family and friends, and just don't understand why the stairs to the basement are positioned so poorly from a getting stuff in and out POV. Whatever happened to straight in? Whatever happened to good old trap doors accessible from outside? That last idea was very common in the neighborhood I grew up in. My sisters house has the basement stairs off a narrow central hallway in her house. For me, no matter how nice that house or others like it is, makes it impossible to ever buy without adding an additional easy access. If the house has a basement, it should be easily used.