Re: Floor leveling
Buy 8 @ 10 foot 2x4's. Cut them to the exact length for the room. Using a chalkline, mark a tapering line from 3/4" at one end to 2 3/4" at the other. See how the difference in width from end to end becomes 2"?. You can't go to zero with sleepers.If you cut the line carefully you now have 16 identical tapered sleepers. Apply a bead of construction adhesive suitable for pressure-treated wood under each sleeper, spacing them 16" O.C. Fasten them down with Tapcons and/or a Ramset/Hilti driver. This will work if you can spare the extra 3/4" at the high side.
Ideally the space would have a finish floor at the exact same height as in the rest of the rooms. So a 2x4 ripped lengthwise may not be enough height, but I'm working with the situation as described.
Remove not the ancient landmark, which your fathers have set.