Do you have favourites you borrowed from libraries or friends ages ago, but never bought and still remember fondly? If you are not much of a re-reader, other books, ones you've owned and got rid of, can be that way too. Though non-fiction for work and hobby purposes is worth hanging on to. (And that's what you'd need if the internet were down in any case, not so much several hundred okayish novels.)
What about the idea of books sitting there unused? You can pass them on to someone who will use it. (Especially rewarding if they are books used for courses or professional purposes.)
You also don't have to do it all at once: start with the ones you'd be least bothered about getting rid of, and do this every few months. If you've got less stuff coming in, that could get rid of several hundred books over a year or two depending on the size of collection.
Unread books: a lot of people say to chuck anything you've not read within a couple of years of buying it. But know yourself: I've rebought or borrowed unread books I'd got rid of a few years earlier.
Ebooks as replacements: they may take up less physical space, but they do still cost money, and the money can't be recouped because you can't sell on ebooks. (Irrelevant for cheapo novels, but might be for a £20 non fiction, depending on your circumstances.)
Are books a big clutter problem in your house?
They are quite easy to organise and store compared with some other things. Is addressing books a step on the way to working on other more complicated clutter? or semi-procrastinating? Or are they spilling off the shelves and in stacks on the floor?
If your income is lower, replacing stuff you might need again in a couple of years isn't as easy - there are articles about how decluttering / minimalism is a hobby for upper middle class people. (Though equally, there are some things sitting idle which can make a bit of money, especially kitchen and fitness gadgets.)
To what extent is doing this right for you & your family?