[gone fishin]

I placed my RO/DI unit after the water softener unit. My reasoning is I did not want hard water scale to build up on my RO membrane.

I would suggest getting a RO/DI unit. You mentioned your parents had the test results so I will assume you are a younger person. You can mention to them that they can also use the RO water for drinking water. Good luck just my 2 cents.