I still don't understand what instances require the use of 'yao', 'wao', 'chao', 'vyao' and now, 'zao'. Is there anyone who can help?
It depends on the word class of the noun. A good overview can be found in the Kansas Univ. Swahili course: https://www2.ku.edu/~kiswahili/, chapter 45. The whole course is downloadable as a PDF: recommended!
Gift and present mean the same. Maybe this only in British English?