I relate so much to this question/situation, from being an outgoing/gregarious introvert (with a low-key family), to being married to a man who's easy-going and comes from a family culture that is quite different from my own (and bigger/more extroverted/with WAY more expectations/obligations). I have had a lot of struggles with this.
To echo a lot of what others said: figure out what is it that you can do that will make the visit more enjoyable. With me, it's been made clear to my in-laws that I'm an introvert and I have limits. So when they visit us, my husband will take them out of the house to do something (without me), or I will head out of the house under the pretense of getting work done (or doing a certain activity). This allows me to be friendly and gracious the rest of the time. So, I might head to a coffee shop or library to do work (and either work or read), or go for a run by myself, or my husband will go out with them for dinner or to show a location they haven't visited. I also make sure not to have visitors to our place for more than a few days, and have my husband take the lead on communication/planning - he is the main host.
It's honestly been a huge struggle for me to be married into a bigger family with way more expectations and obligations than I care for or grew up with. I am seen as being in the wrong/not agreeable sometimes, particularly as my husband is very easy-going and historically has always preferred to keep the peace. This has lead to some painful situations for me where he was putting his family first, and causing pain for me because he wanted to avoid causing discomfort to them. We had to talk about that a lot, and he now makes a conscious effort to be vocal when something doesn't work for us as a couple (vs before when it was put on me). I don't exactly have your problem, since I don't have a problem making sure I get the decompression time I need, but it does mean that I've dealt with negative reactions of in-laws to that, since they operate differently. But it's OK.
If you have a hard time advocating for yourself, perhaps focus on one or two activities to do during each visit and have *quality* time. You can be thoughtful and attentive for these activities, ask questions, show respect/care, and let yourself off the hook from being 'on' all of the time. And at the end/beginning of each visit, frame the visit as 'I'm so excited to have you, especially to have a wonderful time doing X and Y together. I have scheduled obligations, but I care for you and prioritize my time to be able to do X and Y with you.' And booked it with 'I'm so grateful that you visited and we were able to have a lovely time doing X and Y together - it was fun and meaningful, and a priority to spend this time with you.'