Aside from it being the cheapest option (i.e. the lowest down payment) and the reduction in living expenses, it is the easiest way to get your foot in the door, which IMO is the most important part.

Rent reduction until a job is found.  

If it doesn't cash flow, you have limited your return to principle reduction on your mortgage and appreciation. 

If you make all of those changes, your usage should drop by over 30%, with a similar reduction in your bill(not one-one, because there's probably a fixed fee for the connection and then usage charges after that.)

Then lot prices have escalated as there are more regulations every year including endangered species, wetlands, flood plains, hydro-geological studies, traffic studies, and density reductions, that lot prices are often 25% or more of the total package price.

The more you contribute to debt reduction, the faster you eliminate your mortgage debt.

Professionals like myself who work in this field FT, not dabble or arm-chair quarterback, this is all we do, we have universal consensus that there is NO feasible means available for price reduction of real estate.

A survey was done on the property prior to closing.The reduction in value of the property without the guest house is ~50k-75k.The deal and project is a grand slam with the guest house.

If it is really an issue for him and he thinks buying his own stove will solve it and you are okay storing yours let him do it at his cost. no rent reduction. not sure if there is another safety shutoff you can use.

You can also Google the snowball method for debt reduction.