Hi Audie,
I believe I understand your problem, I'm a bit of a hoarder myself but I do occasionally have a fit and throw things out! Here's a couple of suggestions you might want to try.
First off, have a word with the local paramedics, and arrange to borrow a gurney for an hour or so. Take it to the house and show them both how impossible it is to move it around with nobody on it, and that it could mean their lives if the paramedics can't get them to the hospital quickly enough. It's not enough to explain it, wheel in a real gurney and let them see for themselves!
Sounds like a lot of the heavier furniture is surplus to needs, so I'd suggest removing some of that first. Arrange it with your brothers to "modernize" their living space, removing some of the larger stuff and replacing it with smaller, lighter, modern items where needed. Things like chairs that are closer to wheelchair height for example. If you've ever been in a wheelchair, it's a vertical challenge - people standing up are too high, and you tower over anyone sitting on a sofa or armchair. When I was a kid and my grandfather lived with us, my father put two armchairs up on blocks, so anyone sitting in them was the same height as a person in a wheelchair! Consider installing wheelchair ramps on the doorways now - much easier when planned than leaving it until the last second!
Consider taking and selling off some of the nicknacks to buy a couple of hover-rounds or similar, which would increase their mobility tremendously. you can identify some of these as follows:
Set aside a "work area" in the living room, and have them sit down there for an hour or so each day, start going through all the small stuff from the rooms upstairs (which you bring down in batches). They can decide if they need it, if they want to sell it, etc. but the box for "keeping it" is only half the size of the box of items, and insist they write down WHY they want to keep each item. If nothing else, they will have a lot of fun with the memories of items they haven't seen in years!
Get some old cell phones, with no sim cards in them, and put them with their charger in all the bathrooms and any room that doesn't have a phone (they don't have to be plugged in as long as the charger cord is long enough to use them while plugged in). Even though they have no sim card, they can still call 911 in an emergency. Get some orange labels and stick them on the drawer where the cell phone is stored, to make them quick and easy to find. Hide a door key to the front door somewhere outside, and contact local police and fire and let them know where it is. The ideal solution is a fire-box outside the front door. Police and fire both carry keys to these, but otherwise they are secure. I know one lady who kept a key to the front door under a fishing gnome at the pond in the back garden - most thieves won't look that far for it!
You are probably going to meet with things like "I can't part with that, your great Aunt Maude gave it to me", and an easy answer is along the lines of "it would look great in my den/front room/whatever", or "Greg is a big guy and can't find anything big enough to hold him - how about you give it to him?"
My second wife's parents, when they finally retired, also had a lot of stuff accumulated, and a lot of it was farm equipment, but she came up with a novel idea. A new "country style" restaurant was opening up in the area, so a lot of the stuff was sold to them for decoration, including horse-drawn plough shares, balance scales and a lot more! Turned out her folks made the restaurant their favorite hangout on a Sunday, so they were still able to enjoy the stuff while someone else was paying to keep it clean and stored!
The hardest part will always be trying to get them to part with something, so getting them to explain why they want to keep it first will be very helpful. Then you can use an argument along the lines of "I know it's a sturdy old table and might be useful in the future, but if we get rid of it, we can move this sofa back there and leave you some room for your hover-round that you can use now - wouldn't that be better?"
Personally, I don't envy you that task, but I hope that some of the above ideas may work for you, or may germinate into something useful!
DaveyB