Not really a new problem, attaching damped mass under the existing floor will help, so will the insulation, so will adding a new floor with an underlayment. When you finish the ceiling consider using extra mass, dampening and Isolation what is called a room within a room construction. You will need to check the size of the 95 year old joists and their weight carrying capacity before adding a lot of mass. Here is a good read for you.
https://www.soundproofingcompany.com/soundproofing-solutions/soundproofing-ceilings
Yes, shared duct work needs to be addressed but that can be done and your efforts will not be in vain.
https://www.soundproofingcompany.com/soundproofing-solutions/soundproofing-ceilings
Yes, shared duct work needs to be addressed but that can be done and your efforts will not be in vain.