@Virginia231
You can change the "minimum nights to stay" for a certain period in "availibility", "trip lenght" , ädditional requirements" and then choose option "add a custom rule for seasons or specific dates"
If you have the multicalender available, you can do the same (with more options) by creating a ruleset.
it is not possible to do exact monthly/6 monthly reservations, for that a (additional) renting contract is more convenient: You also need to set a monthly discount, otherwise you will no show up in searches for long term stays.
https://www.airbnb.com/help/article/1354/what-are-some-differences-between-longterm-hosting-and-shor...
Best regards,
Emiel