There are 2 components to mitigate when trying to dampen sound: transmission & reverberation.

Challenge - real estate is a fluid business, and not a liquid business. 

As @Roy N. mentioned, The ruxol safe and sound with a double 5/8 sheet rock should cut down on most of the echoing and sound transmission.

The others are more important in terms of fixing a date since my schedule is a bit fluid but happy to add on once dates are set if that might be ok for you.

And the law is pretty fluid on what the requirements would be to take advantage of the primary residence exclusion. 

There are reasons this would make sense:1) You can takedown much smaller units where many of the deals are2) the exit strategies like getting money out or 1031 etc. can be much easier with this structure 3) timeframes can be shorter because the process is more fluid. 

There is a fourplex and two warehouses and a transmission shop.

Hey @Matt McKinney, letting water and other water-based fluids sit on wood or wood-like floors, even just overnight, will cause them to ripple.

Your septic tank holds your crap (literally), your shower and laundry water, and every other solid and fluid coming from your plumbing system.

Such fluid change of ownership can create all kinds of issues and is not recommended.I recommend you do NOT structure this "working with 2 other people" as a joint venture at all, if possible.