I didn't even know Greece had elections, and honestly I don't know anything about these mayors until you posted about them. And it's only their religion, not their political positions or anything. I really don't have anything to go off of, and I doubt anyone else in this forum will. Perhaps ask Greece Travel what they think.
For now, since I literally only know of their religions, I'll just say "Mazel tov" to both of them and wish them the best. That's honestly what you should do, if you care about these regions at all. Jews and Muslims aren't out to destroy Greece, not when they're citizens and they want their nation to thrive too. I looked up the guy from Ioannina (which, I must say, it's weird a Greek person wrote Jannine) and he seems like he'd make a good candidate from what is written about him. Just have faith he'll be good for that city.