wow... now that's a project. Good Luck.

Get a builder to pull the permit. If you do it incorrectly, you will get the red light when you try to sell it.

The run of the stairs must be extended.

There are many code requirements concerning stairs, including the rise and run of each tread, the railing, the termination of the railing, the depth of the top landing, etc. Be sure to check it all out.

Stairs are tricky and are the #1 source of accidents in homes. There are a lot of code requirements that go in to the design of stairs but the basics are max. 7 3/4" rise, min. 10" depth from nosing to nosing, min. 80" clear head height along the entire length of the stair and handrail 34"-38" above the leading edge of the stair (nosing). Typically, replacing older stairs requires lengthening the stair since you will typically add more risers to this staircase. This is usually a difficult exercise in an older building where the original space planning was for a shorter run. Not impossible but fairly involved exercise requiring a design that meets code and a building permit.