I’m looking at executing on a 15 unit deal and using third party PM.My question for those who have done the same, how does the third party execute the various requirements such as leasing & maintenance and how much do you pay for those services?

I am a huge supporter of Market Leader (used to manage accounts for 40,000+ agents across the United States) and have seen many agents have great success with their leads program, but it is expensive.  

I have a 12 unit building that I'm in talks with seller on.

We hired contractors to construct the basement unit and turned 300 square feet of unusable space to a $1,000/month of rental income.

U want your parents to talk to their CPA FIRST.. if they go the development route they are now ( depending on the amount of units) creating inventory.. which will be taxed at ordinary income rates ( very HIGH)if they just sell they can 1031  and move on to something else.. many times when you run the math consider the risks of a partnership.. the sale of the land is far better than thinking your going to make some profit.. 

I cross-list my MTR units on Furnished Finder and Airbnb.

So, the following comes from the perspective of a small-portfolio landlord who is a DIYer who lives close to his units and doesn't want to pay for a Registered Agent and PO BOX.

Electric heaters for apartment units.

However, real estate values (on a national average) havenever gone down over a 10-year period. https://fred.stlouisfed.org/series/MSPUS

The suggestions of getting a 2-4 unit multifamily are great too.