ഇതുപോലെയുള്ള എന്റേയും പല confusions-നുള്ള frustrated ആയ ഉത്തരമാണ്‌ എന്റെയീ മലയാളം വര്‍ണ്ണമാല: http://cibu.blogspot.com/2003/09/malayalam-phonetic-alphabet.html

I have asked this also. My teacher said “kai” is correct, “kayyu~” is not…

That is still understandable, but I think when it is followed by a vowel, it will become “kayy”.

This may be something people might have debated and corrected later. I am out of all these for a long time. Probably some experts might have discussed this, which my teacher was not aware of.

If any Malayalam experts read this, I hope they would comment.