I live in an 1880's Victorian terrace. The upstairs has 3 mismatching stud walls dividing the landing from bathroom and both first floor bedrooms. The one dividing the landing and the bathroom has been put in very badly. The one dividing the landing from the back bedroom is partially decent with a few warped bits at the edges. The other wall is new but a lot thinner than the others. Is it a big job to rip out all of the walls and rebuild them with uniform thickness/door hole sizes?
Is it a big job to rip out all of the walls and rebuild them with uniform thickness/door hole sizes? - Depends on your viewpoint/capabilities.
You will have to make sure the walls are not supporting anything above - roof structure, water tanks, joins in rafters etc. You will probably also find electric and water services buried in the walls.
If you do remove the existing walls you will have a disposal issue with the plasterboard it has to go to designated dumps. I have not yet found a company which will provide a skip for plaster products.
You could board over the existing walls (with packing as required) and modify the existing openings.