Student or Learner
1) how should i ask questions when shopping?
"do you have batteries, please?"
"do you guys sell batteries, please?"
"i am looking for batteries. do you have it, please?"
2) how to address the stewardess during a flight?
"i would like some water, please"
"could you get me some water, please"
how to say if i want to address to more than one person?
i am aware that grammatically we use you for plural and singular.
but, if you are in a group of people and want to address to 2 people, don't you need something else to be more specific?
if you simply say you, how to make clear that you are addressing to more than one person?
"you guys" is what i commonly hear on the movies. is that rude?
It is impolite to say to a starnger 'guy'.
As baqarah131 mentioned: say just 'you'.
(It would be polite to call each by name if you know their names.)
The postings above cover the subject well.
I'd add only that the lack of separate forms for the plural and singular
"you" is a problem even for native speakers.
There are frequent misunderstandings because it's not clear who we're talking to.
best wishes to all of you