If the guy hasn't done a water change in two years, you may have a lost cause on your hands
I mean, all the work you put into getting the water back to the right chemistry and down to a small amount of nitrate and phosphate will go by the wayside unless he commits to frequent and regular maintenance.
Your desire to help this poor soul is admirable, but the first question I would ask him is how does he feel about weekly or bi-weekly maintenance.