WIBTA if my husband and I take the master bedroom on a family vacation

My husband and I are heading to a lake house this weekend with my MIL and SIL (+family). My husband and I, who booked the cabin and thus know the layout, will arrive before everyone else. We are curious if we would be in the wrong to automatically take the master bedroom with the ensuite bathroom.

For context the room is the only one on the second floor. There are two bedrooms on the main floor each with a queen bed and a room in the basement with two twin beds. We figure the kids will want to sleep on the twin beds and that my SIL will not want to be on the 2nd floor so far away from them, thus her choosing a room on the main floor. My MIL is only staying one night, so we figure she would be ok on the main floor as well.

Are we assuming too much?