About Zanzanna, it makes sense to send a second or third son to Egypt. Imagine the other way around - the king of Egypt would never send a crown prince to marry a foreign queen - far too risky to contemplate - better to send a brother who could then be a loyal ally in the future but not threaten the stability of the succession. I suspect Suppiluliuma took into account the likelyhood of something going badly wrong - there may have been parties in Egypt opposed to the idea (in fact I believe that was extremely likely). He probably considered it was worth the risk in case the gambit worked. If not, it would be an excuse to take more from Egypt.