@Pepi12, @Marzena4 asks an important question: do the guests have to share any of their space with anyone
(meaning your parents).
The review that mentions the mother and father living downstairs also includes an incident where the father entered the guest space without warning.
You might need to have a conversation with your parents about when it is appropriate to enter the guest areas uninvited (the answer: never). If your parents feel it is appropriate to enter the guest space at any time, it is obvious why guests will not feel they are getting an entire home.
(And do your parents have their own separate entrance?)