They are super demanding and have high expectations that you will conform to the pattern they have laid down for their own convenience.
It’s not difficult to slip into this annual ritual as routine I know. But only you can put a stop to it. So take a firm lead in changing things now.
When they message asking to book dates for next year, ignore the message….you are busy for now and simply got distracted and forgot to respond.
Some time later, or when they message again, reply in your own time to say that you have both come to the decision that you won’t be hosting next year at all, but are still considering your plans.
Don’t volunteer reasons, it’s perfectly polite and acceptable under all circumstances, CF circumstances or not, to keep it that simple.
If they press you for reasons just say … it’s just a decision we have come to as a couple, please don’t take it personally but no, we won’t be hosting at all next year, we are still thinking about how we want to spend our leisure time budget.
You can still be friends if that’s what you want …be proactive in suggesting alternatives, saying what a lovely change it would make to do something different - eg meeting up half way somewhere interesting, for dinner and an overnight/long weekend, each couple paying their own way of course.
You are under no obligation to respond the same as before to their invitation to invite you again.
If you are really upset by their message to ask you for dates to come again, you can simply say…. No thank you, not this year, we have other plans.