The seller agreed to take it out and remediate the soil.

It always boils down to the main part of the home, and what type of soil was it built on.I have seen 150 year old homes that were in perfect condition and well maintained, these homes usually sat on elevated grounds with good drainage (which limits the movement of the foundation).When a house is built on flat ground and or where clay is present.

@ Dan, Twana, great insights on the sewer scope, as well as the beach sand being used underneath foundations in certain older areas of San Diego. 

Or should it be purchased underneath myself as an individual ?

Find out if you can tear it down, and if you can re-use the foundation, what is the property zoned for and what else could be built there, if it will need any special type of soil samples or other things of that nature that could get expensive, etc etc.

The cold vs hot markets usually boils down to population and demand growth differences and underneath that is jobs. 

However, the sewer is 12 feet deep, runs underneath a set of concrete stairs and then 25 feet into a main city arterial. 

"ugliness".. sure, let's call it ugliness shall we.. well... if it is mine it is called "dried rose petals", fell underneath the house (no basement).

The South Denver/Centennial area is where I would like to focus and there doesn't seem to be too many problems with real estate in this area e.g. termites, soil movement etc.

You do not want to spend time and money and then have the carpet pulled from underneath you.If you can not get both brothers co-operation then you are spinning your wheels.