A stair is a measured job. Rise, going, head height, and how the stringers land. After an interior demolition the old stair is often gone and the opening has moved a little. We measure twice. A railing is not an afterthought on a steep inner-city stair. It has to work with the stringer and the landing.
Repairs are common on houses that are staying: a broken tread, a loose newel, a landing that has dropped. If the structure under it is the problem, we say so. Piers and bearers may need to come first.
If the floor structure is the problem, start on beams and floor bearers. The stair cannot sit on a bounce.
We inspect, then we quote. Photos of the opening, the existing stair, and the hall help. Call 0487 549 909 or send the suburb and a couple of photos.