There have been a number of threads about this over the years, and if you can recruit someone "in the know" to help you it will make things a lot easier.

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If your stepfather was a member of any model engineering clubs, I would absolutely start by asking them for help… If not, if you can contact local clubs they will also be quite helpful.

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If it is all too much to deal with in the time you have, don't go to a house clearance firm. There are specialist dealers/firms who will take on workshop clearances, who will be both better equipped to move things, and more likely to preserve and re-home the equipment with people who value it.

"Home and Workshop Machinery" is the one which jumps out at me, but there are others, they will obviously only pay you a proportion of the full value of the equipment, but that might still be the right choice for you and your family.

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If I can find it with the search function I did post some advice on how to advertise equipment to sell, and what to expect when people come to collect, so you're at least mentally prepared for what can (depending on the size and location of the item) be a bit of a palava, and I'll repost here.