My opinion...
1) CEO should start the talk. Beyond that, it depends on the people (team of CEO/CTO) and subject matter as far as who speaks the most and when.
2) In my experience CEO leads discussion and invites commentary (slides) from CTO as needed per agenda, and this is usually on technology/product design. CTOs (like many engineers) occasionally need coaching on communicating at proper level of detail to meet meeting objective.
3) CEO is responsible for raising money so this person should manage (lead) the discussion as a general rule. A weak CEO in a pitch format is a warning sign for VCs. Obviously though, if a question is directed toward CTO, opportunity to answer should be provided. VCs throw questions from many directions based on their own interests so anything goes. Know your stuff. Know how much time you have to get through it. Believe in it and be ready. Happy to discuss in greater detail.
Good Luck!