Merging text in a list between rown depending on a criteria

Good evening everyone,
I'm new to this forum and I join in order to improve my excel knowledge.

I work in an hotel and I'm having the following problem:
every week we do a cocktail for a part of our guests and I make a list, then I have to separate them by room and print 1 invitation per room with the surname of all the occupants of the room (using the mail merge and several invitation in Word format depending from the sitting and language of the guests).

In the list there are room with 1 guest,2, 3 or more with different surnames.
I need to insert all the surnames of one room in one cell and delete the rows of the same room. This takes a very long time (since there are more than 1200 people and rows) .
Is there a way to manage it? I tried with advanced filter and unique record only but in this way I get all the room but with only 1 surname.
I know it is not easy to understand with my description so I attach the file.

I will greatly appreciate your help because it will save me from many hours of extra work.

Best regards