How big of a deal is it to get from the airport to the city?
No big deal at all. To get to the U Bahn (subway) from the airport, you have to first take a short ride on a city bus.
My in-laws are connecting in Berlin on the way to TLV. In case they CH"V get stuck there for a while because of the strike at Ben Gurion, what are the kosher food options there? Are there even any?
Kosher food?! I'm not familiar, but that airport is so small, some gates are like a mini-prison, there's really like nowhere to go (post security), you're lucky if there's an open store at the gate.. Can't wait for the new airport to open already...
There is a restaurant in the Chabad house, but they are not open the whole day, so check first.