Booking multiple rooms in one booking is possible by adding to cart and filling up the cart before sending in the request to book.
The process is the same for booking and confirming, but instead simply press Add.
You can then do a search again on different dates or with different filters and Add that to the same cart.
When you have multiple properties or the same property at different dates in the cart it will look like this:
Here you can see the, in the same booking cart we have two dates. This is helpful when looking at your bookings overview.