Mrsb, you have my utmost sympathy as there is nothing you can do until the absolute crisis point is reached.
My Fil is a chronic hoarder and your description of your DF is Fil to a T - I read your post to my DP and asked him who he thought I was talking about and he replied "my Dad?".
My Pil's have a 3 bed semi and at its worst it was crammed with boxes, books and junk and Fil would not stop buying or acquiring more stuff as it was: a bargain/makes me look clever/I'll read that/I need it/interesting/ can't find the other 5 of these that I have somewhere etc. He also kept all junk mail by sorting into piles of take the stamp off/envelope for recycling/I'll keep that for reference so I can use it later even if it's 5 years out of date. He also kept jars, milk containers, yoghurt pots, newspapers, toilet roll tubes etc. You name it he kept it. This is probably sounding all too familiar?
My Mil gave up tidying about 8 years ago and started a slow decline into dementia so her last years were spent in a dirty, dusty house where no one ever visited as there was nowhere to sit, the smell was horrid and going in the house made you feel dirty.
We stopped the grandchildren visiting 6 years ago and told Fil why and this had no effect. Nothing had any effect on his hoarding even with the following incidences:
*They each fell down the stairs due to books stacked there - no effect
*Mil fell quite a few times over stuff and had black eyes, lost teeth etc
- Fil cut his leg on one of his own boxes and nearly lost his leg/life
due to the infection it caused - no effect
- Fil has COPD made worse by the dust - no effect
- Fil even took stuff on holiday ('to sort it') and when Mil fell over one
of his piles and broke her leg he drove her 80 miles home
(screaming in pain apparently) and then called an ambulance
because he didn't want to inconvenience of having to visit her in a
hospital 80 miles away - no effect
- Mil had a funny turn (had heart murmur) while being made to turn
the sofa upside down to look for the tv remote and ambulance was
called. Paramedic called DP to let him know that she was going to
hospital for a check up and asked if he was aware that his parents
had had a domestic incident and did he want the police informed?
DP assured the paramedic that it wasn't dv and that the house
always looked like that. The remote was located under a pile of
magazines that Fil was 'sorting' - this also had no effect
- Mil was often ill after eating at home due to filthy plates/cutlery and
out of date food (Fil has constitution of an ox!) - no effect
- We gave an ultimatum 3 years ago that Fil allow us to tidy the house
for Mil's sake or we would all leave them to it.Fil agreed to clearing
the house. We even got a skip and filled it in one afternoon and were
making progress. Fil then said that he no longer agreed with tidying
and that there wasn't a problem. We walked away. - no effect
All of the above has happened in the last 5 years but then last year things changed as the final crisis point was reached. Again DP had a call from a paramedic during the night (DP had POA over his mum's affairs by this point so he was first contact). Paramedic said that Mil had had a funny turn again while in bed but when they checked her over she was riddled with bedbug bites which had caused low blood pressure/ palpitations and they thought that the bites needed treatment and she needed care for possible malnourishment etc. The house was infested with bedbugs. Fil had known for about a month and had been spraying his side of the bed with bug spray but nowhere else. So Mil went to hospital and social services became involved. With their insistence and DP's agreement, Fil was told that she would not be coming home until the house had been treated and that the house had to be cleared of junk to an acceptable standard. So we cleared as much as we could after the treatment while being shouted at by Fil. Mil came home and 4 weeks later the bedbugs were back.
This time we threw out all their beds, bedding, clothes that didn't fit etc and cleared the house of all junk (Mil was back in hospital for infected bites at SS insistence)and had the pest controller back in . Fil was very shouty again but DP, Bil, Sil & I held firm and told him that if he wanted his wife back then he had to comply. He shut up and spent the day phoning everyone he knew to tell them how horrible we were being and how we were destroying his life's work (yes, that is how he thought of it!!). Once we were sure that the bedbug problem had been fixed, we had carers come in 3 days a week to clean the house and to keep some kind of order in the house.
Things are more settled now. My DP spends his time keeping the junk piles under control and the carers keep the house as clean as they can. Fil is less mobile now so he can't go back to full hoarder mode but he is still very messy so we have to keep on our toes and clear his 'sorting' stuff out weekly. Mil went into a dementia care home 9 months ago and died last week after quite happily spending her last months in a lovely clean quiet environment which is something she had not enjoyed for the last 8 years.
In the end the hoarding was stopped by the simple bedbug which gave us the necessary power to take control of the inlaws misery. Fil is now happier in his home and the shame he felt over the bedbugs forced a change over him but we are never fooled into thinking that we can let the tidying go and it is a constant, never ending job for us.
Things only changed once the apex of crisis was reached because to the hoarder, it isn't rubbish - it is treasure. Mrsb, I hope that you can persuade your DF to change but chances are that he won't and he won't have therapy either as he can't admit that the hoarding is an issue. Support your DM as best you can but chances are she'll (like my Mil) back up your dad due to loyalty to him and that's what a wife does when you've been married that long. Pil's were married 67 years and Mil would never hear a bad word against Fil. All you can do is wait and pick up the pieces as things deteriorate as they age.
Sorry that was very long!!