Lizziemeg, you are doing great and I look forward to hearing how the day went since the haulers will have come and removed the things you were getting rid of. By the way, I found personally that the master's degree program was easier than undergraduate!
Jackie, I also agree that Tillie has much valuable advice and example as someone who is not a hoarder but lives with one. I can tell you that arguing, demanding, demeaning, etc. absolutely do not work. A hoarder typically feels pretty awful about themselves and pretty typically is in denial about the state of things. We cannot help it. Something about this illness of hoarding does that. But if you can find ways to build his self-esteem, and to understand what motivates him, you have ways "in" to motivate him to change without any harshness. I recommend reading Matt Paxton's book "The Secret Lives of Hoarders" as it gives examples and advice to those who love hoarders.
You can raise your daughter to be a thoughtful, orderly and clean person by "rewarding" her for any steps she takes in that direction (I mean praise, mostly) and by having her work with you to accomplish things that give her satisfaction.
I also support you in declaring X parts or rooms of the house to be "clutter free" and to defend those areas. The hardest part for many hoarders is their emotional attachment to their "treasures" (which we might call junk). Letting go is like abandoning the person to whom the item is attached (e.g., his mother's things). For some, nonanimate objects have "feelings" and there is guilt about abandoning those items. For some it feels like they are abandoning part of themselves, literally. For many of us, getting rid of things means letting go of dreams of what might have been or could have been or ought to have been. Even "seeing" a mess can be nearly impossible for some of us. It just doesn't register as that.
For me it helped to take "before" pictures, but that for me was because I was more a person of squalor than a hoader (although there are overlaps). Looking back now that the major cleanup is done, I am dumbfounded by just how bad it was. Ugh. But for me a reward is the after pictures!
Come back, keep reading, asking, read books and look online for books that might help. It is such a new field (although I am sure actual hoarding is not a new phenomenon) as yet. If you can, watch Hoarders and pay attention to what Cory Chalmers, Matt Paxton and the organizers and therapists say and do. They are outstanding in how they work. I believe the show can be seen online, too.