@Laura2592
I have a house that sleeps 8, but I start my base price at 2. I have 4 bedrooms.
I say in the listing and in the house rules, and they "what's available section" that the whole house is free for them to use, but that depending on the number of guests, some bedrooms may be locked off to help 'minimise excess linen charges" for the guests.
I also ask the guests in advance how they want the bedrooms set up. So if two book and they are two co workers for example and they ask for 2 rooms, that's absolutely fine, I'll have 2 rooms open. I think getting the guests to nominate how they want things up front also helps - some actually say things like "we wont' need the other 2 rooms"
I'm not a seasoned traveller but I have stayed in a number of other airbnb's that did this, and I found it perfectly acceptable as a guest ( and I was a guest long before I was a host). Vacation stays and units in apartments also often do this in my experience. I've only travelled in Australia, the UK, a bit of Europe and that was standard everywhere I went.
I have been doing this as a host for over 18 months and no one has ever complained, but I make sure it is very clear to people who are only booking for a couple ( 1 room) - I might say in the post booking message something like "I normally lock off the unnecessary bedrooms, but I'll leave one unlocked , so you can still get access to the second downstairs deck in case you would like to use it. That way it looks more like I am offering something extra, rather than withdrawing something.
I can't say I personally agree with the other voices here saying you must give all access if you have listed the whole house. I think so long as you cover yourself very clearly in your listing and communication and the guest does not get any unexpected surprises, all should be well.
The other option is to leave the "spare" bed with a base pack of a protector and a cheap coverlet so it looks tidy so it can still be laid on, but does not invite sleeping in. I never have beds made up with linens until the day before a stay, and then only the ones that will be being used - too much potentially to go wrong.
Just my opinion