1.already
adv.
By this or a specified time; before:
早已，已经到现在为止或到某一特点为止；先前：
The children were already asleep when we got home.
当我们到家时孩子们已经睡着了
So soon:
如此之快：
Are you quitting already?
你这么快就辞职了吗?
Non-Standard
【非标准用语】
Used as an intensive:
马上，这就用作加强语气词：
Be quiet already. Enough already.
安静些。够了。
用法：already
[表示现在或过去某时已发生的事实] 已经, 早已, 业经
He had already gone (when I arrived).
(当我到达时)他早已走了。
[问句或否定句表示惊愕、意外时]还(没有吗?), 已经...(吗)?
Have you eaten your dinner already?
你已经吃饭了吗?
--------------------------------------------------------
2.yet
adv.
At this time; for the present:
现在；目前：
isn't ready yet.
现在还没准备好
Up to a specified time; thus far:
迄今直至一特定时间；至今：
The end had not yet come.
到目前为止还没有结果
At a future time; eventually:
将来；终必：
may yet change his mind.
终究会改变他的想法
Besides; in addition:
另外；除此以外：
returned for yet another helping.
尚且还了一份礼
Still more; even
更，甚至：
a yet sadder tale.
一个更悲伤的故事
Nevertheless:
然而：
young yet wise.
年轻却很聪明
yet
conj.
And despite this; nevertheless:
仅管如此，虽然：
She said she would be late, yet she arrived on time.
她说她会迟到，但她却准时到达了
用法：yet
In formal style yet in the sense “up to now” requires that the accompanying verb be in the present perfect, rather than in the simple past:
在正式文体中， yet表达“迄今”这一意思时，须与现在完成时动词连用，而不是简单的过去时：
He hasn't started yet, not He didn't start yet.
他还未开始而不是.他未开始.
already用在疑问句中主要是根据肯定句的提问。
参考资料：金山词霸