Nelliemoser
The problem here is more than clutter. It is a longer term habit of not seeing your rights. It's his own issues with holding onto the past and fear of what might happen in the future. You may be content with what you need/have now, he isnt. Nagging and resentment and anger just make someone dig in their heels.
A multi-point, and probably multi-year plan:
Current space.
Curating a Collection, not hoarding junk.
Issues with the past
Issues with the future
Current space: if your stuff is sorted, point out that the house and property is half yours, and if you chose to leave your half unstuffed, that doesnt give him the right to fill it with his. Nor does he have the right to fill beutral zones, like the corners of rooms or the dining table. Designate his main area (sheds, garage, half the garden) and areas in each room. Be ruthless about defending your turf, and neutral zones. But other than helping display or insisting he dust the stuff on his shelves or other areas, IGNORE his junky bits. not easy, but you really must let his half be his half. (Well, his third, ince you account fir the neutral zones). If you never get past this stage, at least your home and property will be 2/3 bearable.
Collecting vs. Hoarding
Like many hoarders, he probably thinks of himself as a collector. Someone with a fine eye for quality or rarity, especially at a good price. He thinks of these purchases as an investment, and himself a bit of an expert. Use this to your advantage. Play along.
Past issues: can you bring yourself to admire one sub-collection? Which you can help him create an actual display of on his shelves in your main room? And then carefully store the rest, labelled? Or (hope against hope) then discard the junky bits, and only keep the fine collection. Get him to talk about these things, make a point of getting the kids and grandkids to ask about them. Whatever is driving his need for those books, or tools, or trains or cars, is probably an interesting thing for at least one of you to know about him.
Next year, pick another sub-category. Turning each pile into a proper collection, giving him a chance to share the collection, and share whatever is driving his need to collect, might help him appreciate the joy, as Marie Kondo says, each item brings him, and realize that some items dont. That new joy can be had by returning the bits that serve no purpose to his fine collection back in circulation, for those who might need parts, or be happy with that lower grade item. Or maybe, once he starts treating some of his collecting Very Seriously, then he will be less interested in other parts and can be convinced to let someone else have the joy.
Future Issues: does he have notions of you, or the kids and grandkids sorting it out and making a fortune because so much of this is/will be valuable? You, and they, need to make clear that, if he thinks there is cash value in any of it, he needs to deal with cashing in the asset. He is the expert and needs to ACT if he wants you to benefit. Because you wont have the physical or emotional strength, and the kids and grandkids simply won't have the time, even if they do have the interest. Everything will go to charity or the tip. Even if you try to sell it, you could be easily tricked by anyone who seems knowledgeable, but is not honest. He needs to protect you from this possibility by reducing his collections to their valuable minimum, having them valued, documenting them, documenting the best way to dispose of them. If his joy is in feeling like he is caring for you by providing this future asset, he needs to actually make it usable, by cashing in himself, or making it very easy for you to do so.
It may help, to begin with being quite noticeably busy curating your stuff. Noting that this thing is finer than the thing you have, and so, you will replace one with the other. Or noting that a gift was a joy to receive, but is unnecessary, so you will pass it on to charity. Even if that thing is a just black cardigan, or a new sugar bowl.