When you charge under market rent, the IRS deems that you do not have a profit motive and, therefore, disallows all rental expenses. 

It's simple enough to make a row for income, and another for expenses, and then subdivide those expenses, and add them up in the total expenses cell and then subtract the gross income from those total expenses to get my net.

@Eric Coats, to answer your specific questions, estimating expenses are pretty simple. 

With the fund I used, they had a month where they had a few defaults, the return was a bit lower, and they sent out an email apologizing for the lower yield. 

Regarding price, do you have any suggestions on how I can get him to agree to a lower price?

Once we lowered the price to $1 less than everyone in town we filled right up.

Alternatively, your in-laws could partially gift the property by using the annual gift tax exclusion ($34K per couple annually), lowering the sale price and their taxable gain.

Better to concentrate on decreasing expenses and saving for now. 

We discovered problems that required a lot of work and significantly reduced the property’s value, forcing me to lower the price.

Are you looking at the maintenance/repair costs of the homes once in place, W/S/G costs. septic expense if applicable?