I am working on a project to open up my stairs in my 1901 built twin house. My joist run the full with of my house from stone foundation to stone foundation except for around the stairs. There is a 2x12 that runs along the stairs and the joists are level with this and nailed into it. I have a 4x4 under the end if that on both ends both in the basement into cement and on the main floor. My question is if I take out the support at the first step on the first floor and brace it with a 2x6 to carry that load out to a wider point and then down, can I just bring this down onto a joist, or do I need to support under the joist to the basement floor to carry it down again.

It seems like the way they tied them all in with railroad spike looking nails 100 years ago holds it up pretty well, but I'd rather be safe. There was no support under the basement corner when I bought the house and I added one.

Some pictures may help. You can post pictures here by clicking on the add attachment link below the text box in the Post A Reply box. Even with pictures we may not be able to tell what's needed without seeing it in person.

Agreed that a picture would help, but be aware that while lots of us here do have structural knowledge it is not a good idea to get all your structural advice from this board.

From what you have said, you currently have the strongest thing possible with the load on those 2x12's being transferred by bearing directly on posts on a footing. I cannot imagine any case where you could use 2x6 to brace in any direction so that you could remove one or more of those posts. Any header extensions or bracing will need to be at least as strong at the original 2x12.

I would advise you to find someone local to come in and take a look at what you have and what you want to do.