Hello Andressa! I didn't know what the context difference between these words and if we can put them into the same phrase too, but after searching a little bit, I've found these (shallow) definitions:
Yet is generally used in the final of the phrases and never is used on the negative form.
Still is used to refer to situations that happens in the present time. Used in affirmative phrases or questions.
Searching in a few forums, I reached the conclusion that we'll have to utilize only one of these words to say "enquanto", not the two of them at the same phrase 'cause which word has a different use depending of the context.