What is the difference between "rwyt ti"and "wyt ti"?
Sorry question again.
In essence, they are the same - just mutated, depending on if it is used as a question or in the negative. [As MrGWallCymraeg points out, I was incorrect - it is not a mutation. See his great explanation below.]
Rwyt ti = You are.
Wyt ti = You are?/Are you?
Dwyt ti (ddim) = You are not.
(also, never be sorry for asking a question! that's how we learn :) )