The short answer is yes, depending on the property, you may be able to access up to 4 hotel rooms on your mobile key.
If the hotel has this option activated, they will be able to add the additional rooms to your mobile key.
The caveat here is, once the rooms are added to your mobile key, you will need to share your key with the guests in the other rooms. Please remember there are only 5 max mobile keys. your main key and then 4 additional keys can be shared.
Once the key has been shared, everyone that now has a mobile key will have access to all rooms. This is not a pick or choose, if you have 3 rooms on your key and share it, then the other additional guests will now also have access to all three rooms.