Please do not leave, lend or give a key to your in-laws, if you do they will have it copied as soon as possible, and they will not respect your home or your things as they obviously don't respect you.
Do you visit these people as often as they visit you OP? If not - probably with the exception of his actual parents - can you email each one of them, and say that actually you are getting far too many visits from their family as a whole, that you appreciate that you live in a handy area for x, y, and z, but unfortunately you are finding the collection of visits too much, and that your home cannot be available to them whenever it suits.
You can tell them that you don't want anymore surprise visits, and that if they wish to make a surprise visit they need to have arranged accommodation elsewhere eg aTravel Lodge, or Premier Inn. You can be truthful and say that your husband does not agree with you you telling them these things, as it embarrasses him and makes him feel awkward, but that it is also your home, and all the visits are making you feel anxious and uncomfortable in your own home.
You can add (if it is true, but please don't if it is not true) that you love them, and really enjoy seeing them when you have had at least - let's say - 2 weeks or a months - notice, so you can make any plans that you OP feel are necessary, and that will help you to enjoy their visit. You could also say that you understand that they don't mean any of their visits to make you uncomfortable, but even if they offer to make up their own beds when they arrive, and will buy and cook their own food, you are still left feeling extremely stressed by the unexpectedness of having guests in your home.
If they accept all of that, you can thank them for their understanding, and say that you are looking forward to seeing them at any future date and times arranged between the both of you.
If they don't accept that, then you will need to enlist the 'help' of your husband (aka do what he should have done in the first place as they are his relatives, and they are making you miserable), and get him to tell them exactly the same thing as you have, but definitely including his parents this time - unless they are much more considerate than the rest of his family, or are, and always have been, both brilliant parents to your husband for his entire life, and now to you as well, now that you are their DiL.
If your husband refuses to do this, then I am afraid I have to use the well worn phrase that
"you have a DH problem, rather than an in-law problem".
Good luck with getting this sorted OP, dealing with in-laws is far too often one of the biggest causes of arguments within a partnership - and I am an in-law myself now who tries to be as supportive as possible, but without becoming overbearing or a burden. I am sure that I don't get it right all of the time! I just hope that someone will point out to me when I have overstepped the mark, so that I can apologise, and try to get it right in the future.