You can’t force someone to sell you something (unless you are the Government)
If you and the other owners enjoy the land and the lovely view, which you are entitled to do as it belongs to all of you, then that is great. You are under no obligation to agree to sell common property to someone, or grant them exclusive use (refer below).
If the new owner wanted to buy the common property this would require a 100% resolution in favour by the owners.
If the new owner wanted exclusive use then that would require a special resolution of the owners, i.e. 75%.
This doesn’t include all the other legalese/paperwork etc. that would need to be done.
So if the new owner says they won’t move in until they get a slice of the common property, that’s fine!