My parents house is also extremely cluttered, my mother also having depression. The only difference is that theirs IS approaching "Hoarders" status. There's actually been a few episodes I've seen where I think "hm... well that doesn't look SO bad".

With my parents kind of mentality they legitimately believe that they can sell their things rather than just throwing it away. In some cases this is true. Thankfully, I turned my father on to Craigslist and he's starting to at least clean out one of his barns. (He had to build two full size barns and was considering a third.) My mother... well that's another challenge that I haven't quite worked out yet. I tried suggesting easy easy cleaning products. Like those disinfecting wipes, or Swiffers. I even bought her a Swiffer but she never uses it. I'm in the same boat. Don't really know if there's anything we can do about it.