Why do you want a straight staircase? Most want it because of the view in the hallway/foyer/stairwell, which in your case is eliminated due to the halving and division of the hallway; others want it for comfort, but I don't really see that because of the proximity of the opposite walls on the upper floor. As I already said, I share kbt's opinion. Also, I don't think it's successful: one child walks the entire hallway past the bedroom, the other falls down the stairs when eavesdropping at the parents' bedroom. It is always a small challenge to build a straight staircase in a square - mostly it results in big compromises. What prevents you from turning the staircase 90 degrees at the top, for example? But I admit: this won't change much, but maybe it's a possibility for a fresh start without rotten bridges?