The buyer's agent wants us to sign the home sales contract first, and then work out the details of the leaseback agreement later as an addendum.

You might think you know what you and the soon-to-be ex will work out, but a judge could overrule that if they wished. 

In another state the ratios work out.

They use appraisers that screw a deal by way under-valuing a property.I've found a couple decent ones lately...but only time will tell if they actually work out.

We had to buy a distressed property to make the numbers work out here.

Are they more trouble than worth or can the numbers still work out?

You just need to work out the details.

@Marky Suazo, we've been looking for a few months now and noticed that 3-4 family homes are hard to come by as it seems inventory are majority duplexes however that is what we're looking for as the numbers work out better with the extra unit.  

This is not to say, don't have backup plans if plan A doesn't work out, but rather to keep your focus on plan A UNTIL it doesn't work out.

The 2nd lines are what I’m concerned that you would have to inherit them or work out a settlement with them after your deed is recorded but if your saying they don’t survive the foreclosure as long as they were made aware of the foreclosure by the 1st lien holder than that’s great.