Only if you use the balcony rail as a tightrope.
Not at all - you'd have to physically want to climb up and jump. They all have strong railings that you can't just fall through. It's very safe.
All Ships and liners are fitted with protective rails, both on deck and on the balcony to prevent you from falling. You would have to climb over them to fall.
No not at all, the ships rails are very high and all gaps are covered.