Uses and differences between: Still, yet and already.
Meaning: still, yet (positive phrases and questions)
Position: Before the main verb after is, am are, was, were
Use: Report follows or still something happening in a given time
Meaning: still, yet (negative phrases and questions)
and (positive and negative questions)
Position: Normally at the end of the sentence.
Use: Indicate if anything has happened until the present moment.
Restrictions: Depending on the use, not used in the past (with auxiliary verbs was not, Were not, did not and Had not)
Meaning: and (positive statements)
and (questions to indicate positive surprise)
Position: Flexible: before the main / verb after is, am are, was, were, or at the end of the sentence.
Use: Report something already happened before the moment when it comes.
(For "and" in negative sentences, will "anymore" or "now" for example uses: They no longer live here -They do not live here anymore / now.)
Note the following examples to understand the above discussion: