Here's my suggestion: Καλώς ήλθατε στο σπίτι του κυρίου και της κυρίας δημάρχου του Μεγανησίου.
Somebody else might come up with something more sophisticated along these lines, as there are a couple of issues arising from the gender of the Mayor, the genitive case of Meganisi, as well as the register of your text, which might render ''στην οικία'', ''στην κατοικία'' or ''στο σπιτικό'' more appropriate than ''στο σπίτι''.
Can you give us some context?