Otherwise, depending if they are side by side or up/down units, spray foam insulation (high grade purple stuff) is very good at sound proofing or using resilient channels with soundproof drywall and Roxul is good.Here's an in-depth site I found: https://www.soundproofingtips.com/soundproofing-materials/

The entire home is spray foamed from the roof line to the basement.

The entire home is spray foamed from the roof line to the basement.

Smart choices for finishes, foamed the house top to bottom, high efficiency appliances.

For example you can foam fill the box sills (where the house sits on the concrete walls), which is a huge entry point for mice and inspects, plus it greatly improves energy efficiency. 

I also saw 2" thick polystyrene foam insuation in 4 by 8 sheets that could be attached to the ceiling easily and wouldn't look pretty but might function if its sound deadening qualites are effective.

If the sellers are asking to much thats OK; 1. you make new friends, 2. show them how you can solve their problems, 3. show them their alternatives, 4. keep in touch with them when they initially say no, 5. follow up and renegotiate (may take 2 or 3 negotiations), 6. then once the seller(s) have seen they have little other options they will call you back.

You can also put foam gaskets behind receptacle covers.

Have some vacants I am reconditioning to rent out.Looked at carpet.Found a happy medium at .80 sq ft.and 8 pound plush scotch guard pad at .85 sq ft.This is at Home Depot with a very low installation fee of around 35 bucks.Conversely found 12 by 12 ceramic tile for .56 sq ft.My thought process is too install the tile all the way through on the main floor and use carpet just on the stairs and the 2 bedrooms upstairs.Has vinyl down stairs now but actually cost more than tile and get ripped and messed up.Tile would seem to take more abuse and last longer.I can get cheap berber type carpet for .48 sq ft and cheap 6 pound pad for about.49 sq ft. but I am trying to make it look nicer and not cheap.This is why I wanted to spend a little more on a nicer pound foam pad versus rubber composite.I asked about the Home Depot bid room and the sale person said he could submit but the bids are getting rejected as the carpet is already priced so low.Says HD is getting away from the contractor bidding wars to try and get the price down etc.I checked with prices versus Dalton Ga (carpet capital of the world and the prices were just as good or better.HD is measuring the units for free for me tomorrow.On the tile how much is the grout and the bonding agent for the tiles to the floor??

I had a property manager (PM) who supposedly ‘took care of things’, but the way they did so was to open my check book for me.So, for example, when the doors started to stick a little as the newer home began to settle (common), the PM called a handyman to take the doors off the hinges, shave them down, and re-hang them for $300.