There have been times I booked a connecting cabin for just 2 of us. It would never be my first choice but, if it's the cabin type I want, in the location I prefer, I don't worry about who might want/need(?) the cabin I've booked.
Why anyone would think I should change cabins because their decision to book after I did interferes with their plans is beyond me! IMHO, that's being mean & selfish!