Hi and good luck in your effort to study Modern Greek!
I think you mixed up two different structures of the verb "έχω".
1st structure
In this structure "έχω" means "I have". Τhe verb can be used in all persons (έχω / έχεις / έχει / έχουμε / έχετε /έχουν). It indicates possession.
Example:
Η Μαρία έχει έναν αδελφό. = Maria has one brother.
In this phrase "η Μαρία" is the subject of the sentence in Nominative case. The verb is in agreement with the subject in person and number (third person singular). The object "έναν αδελφό" is in Accusative case.
Other examples:
Εμείς έχουμε πολλά παιδιά. = We have many children.
Αυτοί έχουν ωραίο σπίτι. They have a nice house.
Your sentence:
Το ξενοδοχείο έχει ασανσέρ. = The hotel has a lift.
Το ξενοδοχείο-> subject in Nominative Case
ασανσέρ -> object in Accusative.
2nd structure
In this structure, we use the verb only in third singular person (only έχει and not έχω / έχεις etc.)
Its use is idiomatic. It means "there is" or "there are" and it can be used instead of υπάρχει / υπάρχουν ( there is / there are). It is always followed by Accusative Case (object). Phrases with "έχει" in this idiomatic structure do not have a subject.
Example:
Έχει ανθρώπους εδώ; = Are there (any) people here?
ανθρώπους is in Accusative Case, because it is an object. There is not a subject here (as I told you before, this is an idiomatic use of the verb "έχω").
[The same phrase could be " Υπάρχουν άνθρωποι εδώ;"
The verb υπάρχω is always followed by Nominative Case, because it takes a subject and not an object.]
Your sentence:
Στο ξενοδοχείο έχει ασανσέρ. = In the hotel there is a lift.
"στο ξενοδοχείο" is neither a subject nor an object. It is a definition which indicates place, that's why it is translated "in the hotel".
"ασανσέρ" is in Accusative case, because it is an object.
Another variation of your phrase would be:
Στο ξενοδοχείο υπάρχει ασανσέρ. = In the hotel there is a lift.
In this last sentence, ασανσέρ is in Nominative and not Accusative case.
