The first thing to do is have them checked for UTI ( urinary tract
infection). This is far and away the most common cause of improper
urination.

Where are the litter boxes? Old cats may not be able to get up and
down stairs as easily as when they were younger. How many litter
boxes? There should be one for each cat plus an extra. Are the boxes
kept clean?

Are they neutered? (They are probably too old to do it now if they
are not.)  There's a difference between spraying the walls ( male
territory marking) and peeing on the floor. Do you know which they
are doing?

BarB

Seeing as they are senior citizens, I suggest your friend have these two
seen by the vet. Cat's will often urinate inappropriately when they have
medical problems.