Until someone mentioned it was a semi, I assumed it was a buy and tear down.
It needs an enormous amount of work but I would agree with blocking off the lethal doors upstairs and making those rooms into two en suites.
The unlabelled room off the dining room could be a downstairs loo and the current shower room made accessible from the kitchen to be a utility. The loo could be accessible from just the utility since I wouldn’t want a toilet directly off the dining room.
You wouldn’t need to move walls which would save a bit, though I assume getting plumbing to upstairs wouldn’t be cheap.
Of course, the overall cost depends on how bad the house structure is. If the hole in the floor is rot, it could be very expensive.