I recently wrote a post on handling heirlooms for a Tuesday Trivia, which I'll paste below:

We get a lot of questions here about personal heirlooms and what to do with them. There are basically two options.

The first is that you donate it to a museum/archive. My view with this is that it's best to start at the smallest and most local museum and then work your way up, for two reasons - one, because big museums are less likely to want your stuff unless it's really exceptional (do not offer your great-grandmother's wedding dress to the Smithsonian because you know they collect historic fashion), and two, because the small museums often need good items for their collections, particularly if they have relevant provenance. For instance, if you have letters between your grandparents during WWII, you can offer them to the town/village museum or historian's office, should you have one, then try the county museum (should you have one), then try the state/province museum (should you have one) ... Then it's a good time to try the Imperial War Museum, or various World War II museums. Others may disagree and suggest going in the opposite direction; my viewpoint is shaped by having worked for many years in smaller local/regional museums.

The other option is that you keep them at home. This is fairly easily done, and Gaylord Archival even has a section of their website aimed directly at family history collectors these days. The main concerns are:

• minimize handling of the materials - make scans or good copies if you can, for letters and papers, and look at them instead
• minimize light exposure - all light is damaging to paper and fabric to some extent, and the damage cannot be repaired
• minimize fluctuations in temperature and humidity - about 70F and 50% relative humidity is a good goal to aim for, if possible, but the main thing is to avoid having the humidity go way up and down in a day
• flatten out paper objects as much as you can and, conversely, try to pad out and support three-dimensional objects
• use buffered archival tissue with plant-based materials like linen, cotton, and paper; use unbuffered archival tissue with animal-based materials like silk, wool, and leather

OH. The other thing I was going to discuss was deaccessioning.

You should be aware, if you successfully donate an item to a museum, that they may someday have to remove it from the collection. They may not! But they also may, potentially long after you're gone. This is not done because the people working there "don't care about history" and they're not callously throwing things away - usually it's done because objects are not relevant to the collection, are in bad shape, have turned out to be fake, or there just isn't any room. (Occasionally it's done unethically to raise operating funds. This is pretty rare, though, because it's so bad and everyone gets mad about it, and it's typically just a few very high-value pieces.) You should not donate your material if you want them to never transfer it to another institution, because they can't guarantee it. It's possible to put a restriction into a deed of gift, the contract you sign when you donate your items, but the likelihood of a museum agreeing to include that restriction rather than just turn down your gift is very very very low.

I would say that in this case, you're very unlikely to find anyone who wants these books. Eighteenth-century books are not inherently valuable - in the scheme of things, they're not that old, and as they're from the time of commercial printing there are most likely many many extant copies of these texts available.