The key is that these questions lead to good follow-up questions. "Oh, you don't like memory management in C++? How do you mitigate the downsides?" "Neurolinguistic interpreter? What language did you use? Walk me through the core algorithm."

These always help with your #1 and #3. Nobody ever knows if anyone will do the work, but it's pretty easy to determine whether or not they'd be able and how they'll approach it.