@Shawn Ryan I wouldn't bet the farm (but I'd bet the cat*) that she's going to end up leaving money on the table if she sells on her own.If she finds her own buyer, it's highly unlikely that she has the person who is willing to pay the highest price for the property.  

We pay for landscaping and the oil bills, which is roughly another $300/month averaged over the year, leaving us with a $600 month ‘profit’. 

It also means you don't have to worry about them leaving 

Your plan is to provide separate water/sewer for your two legal lots, and leave it at that.

Is there a huge amount of work to turn them over if they did leave?

I'll leave it at that.You are just incorrect.

(If anyone asks me to leave them alone, I honor that.) 

I can only paint and leave all other leaking toilets and broken lights to other people. 

I always highly recommend removing any lead pipes in a home or building and replacing with PEX or copper.As far as asbestos which is usually insulating pipes or old duct work ( very rarely have I seen it in walls or in attics for insulation) I usually just leave it alone and not disturb it unless being told by someone to at which point I take the same steps as I do with lead

That leaves you with $1800.