The "attic" has a large knee wall in the plan.
I do not see a knee wall here that extends beyond the parapet height. I do not see the wishful thinking of a development reserve even remotely verified here, and certainly not proven simply by creating standing height at the stair exit.
Two floors are being discussed here, although 4 floors are planned.
If the basement is still current, I see not only the knee wall but also the stairs to the attic as superfluous. Then I would insert a treehouse level in the children's rooms, design the bedroom as open to the rafters, and create a crawl space above the dressing room and possibly the bathroom, done.
Sorry, but I have to say this: this is the point where you stop tinkering with the initial concept and throw the whole thing in the trash. [...] — just don’t be squeamish. Tear it apart and start over.
An amateur plan remains an amateur plan, even if you involve a draftsman (and he incorporates hints from a structural engineer). But the Pyrrhic victory of pushing this amateur plan through against all reason in the world (and even if the end is "reaches the courtyard with great difficulty, the child was dead in his arms") is the house builder’s heartfelt honor—almost no herb can combat that. Especially not if you have found a house as a template that was successfully built around the desired staircase...