With the data set out as indicated, then provided you have separate fields for title and both parties have the same surname, you could use
Merge Many To One to create the letters.
Sort the data on the number field then use
Dear { MERGEFIELD "Title" } { MERGEFIELD Last_Name }
and select Title as the child field and 'and' as the child field separator
It would make it a much simpler process if you modified the data (or derived a new worksheet) to have the occupancy data on a separate line for each room i.e. instead of having separate lines for each occupant, you have separate lines for each room. Then it becomes a simple letter merge with the second occupant optionally inserted into the salutation.