One of the local churches in our town built a school on pirex (i don't know how its spelled either). Pirex is a type of rock that is not stable. It shifts and allows the structure to move.
The school was closed after 20 years because repaires to the structure would cost too much. The builder should have tested the ground on the building site better and the school would have never been built. The whole buildingg sufferdd from lifting and buckling areas of the ground caused by pirex or pyrite (some kind of rock the structure was built on).
I feel sorry for your friend, becanse if the house is built on this type of rock the problem won't go away. Talk with a structural engineer about structures built on this type of rock, how to identify the rock, and possible solutions. You may want to not say anything and move?