"In my city, there is a Christian church and a Muslim mosque."
Translation:Στην πόλη μου υπάρχει ένας χριστιανικός ναός και ένα μουσουλμανικό τζαμί.
In this case, yes. (But both singular and plural are used).
But keep in mind that's not always the case. It depends on whether the nouns are independent or not.
exp. Hamburger and fries is my favorite food - Το χάμπουργκερ με πατάτες τηγανητές είναι το αγαπημένο μου φαγητό, όχι φαγητά. They are not independent from each other, so you use singular instead of plural, both in English and in Greek. ^.^
To Dimitra's comment that both singular and plural are used, this might be because the sentence can be interpreted two ways: Using "there is", the second "there is" is implied and thus not needed, i.e., "In my city there is a Christian church and [there is] a Muslim mosque." When using "there are", you are referring to the two buildings collectively, and thus there is no implied second "there are". ... There are folks here that are far more versed in the rules if grammar than I could ever hope to be, but that is what I see as the reason both are correct.