Let's say I want to say 'tonight we can eat chicken', in the sense that it's possible (perhaps I've bought some chicken).
If 'we' is a group containing both me and people who are senior, should I say
우리 치킨 먹을 수 있어요
or
우리 치킨 드실 수있으세요 / 오늘 밤 우리는 치킨 잡수실 수있으세요
...or should I avoid talking about both me and my seniors as a group?
You do not refer to a group that includes yourself in honorifics. (Basically, the rule of not honoring yourself trumps the rule of honoring the others.)
Arguably, you address (speak to) such a group in honorifics.
It may be easier to start with reference in isolation.
Example 1
You have arrived with your parents at your sister's house and her young daughter says have you had lunch? You would say:
우리는 안 먹었다. (We have not eaten. / We did not eat.)
Speaking only for your father you might have said:
할아버지는 안 드셨다. (Grandfather has not eaten--i.e. grandfather to the child.)
Or about your parents:
할아버지와 할머니는 안 드셨다.
Let us say that 하시다 is an 'honorific of reference' for 하다 (or that 시 is an honorific of reference), meaning that honor is given to the person spoken of. Then, the above examples show that you use honorifics of reference when speaking of an elder (or a group of elders), but not when speaking of a group consisting of an elder and yourself.
Let us say that 합니다 is an 'honorific of address' for 하다 (or that -ㅂ니다 is an honorific of address), meaning that honor is given to the person spoken to. The above examples do not include any honorific of address because you are speaking to a child.
Example 2
We now mix reference and address.
You arrive at some event as part of your district's delegation, in which you are the youngest member, and have to fill out a form. You ask the delegation:
저희는 제1군입니까 (or 제1군인가요)? (Are we class 1?)
There is no honorific of reference in '입니까?' because you refer to a group consisting of an elder and yourself (the same result as in example 1). Compare: '선생님들은 제1군이십니까?' (You gentlemen are class 1?) This does have 시, an honorific of reference, because you are not in the group being spoken of.
There is an honorific of address ('-ㅂ니까') in '저희는 제1군입니까?' This might be characterized as your using an honorific of address in addressing a group including yourself, or as your addressing the group minus yourself. ('Arguably' at the top of this answer is a reference to this bit.)
'저희' as opposed to '우리' is rather complex. If you were referring to yourself and a same-age friend in addressing another same-age friend, the two of you are 우리. If you were referring to you and another pupil in addressing a teacher, the two of you are 저희. But a group consisting of yourself and an elder is also 저희 when you address that very group. It works rather like 말 vs. 말씀.
Example 3
As you suggest, the easiest way to handle a group consisting of your elders and yourself is to exclude yourself. If you were guiding a group of elders you may say:
선생님들은 이쪽으로 가시죠 (< 가시지요 < 가시다 < 가다) . (Gentlemen might go this way--as spoken to them.)
You will go with them, but have been excluded from 시, the honorific of reference in 가시죠.
The honorific of address 죠 obviously goes to the addressee.
Example 4
You may get something odd like:
저희는 닭고기로 하시죠 (<하시지요 <하시다 <하다). (We might take chicken.)
Here I think you have been dropped somewhere between 저희는 and 하시죠. The honorific of reference 시 only goes to the other members of the group. You are really suggesting that they have chicken or asking how they felt about it.
The honorific of address 죠 obviously goes to the addressee.
To complete the example, the correct thing to say would be (removing the honorific of reference):
저희는 닭고기로 하죠.
What you wanted to express in your question can be modeled on this as to 저희 and the form of verb.
One complication though. An explicit reference to 'us' (저희) would most likely disappear unless there was another group, say some other tour group in the airplane. But once that happens, the sentence will seem to be about the group minus yourself, which will tend to restore the honorific of reference, i.e. take us back to 하시죠.
On your sample sentence, I believe it would always go '드실 수 있다.' That is, saying 시 one time in 드실 suffices. Repeating it for 있다 overdoes it.
Last, you may be thinking of 'can have' as a polite form of suggestion. I don't believe that translates well into Korean. It would just sound like a statement about ability. You need to find a Korean way of suggesting, if that's what you have in mind.
You cannot use all of them because of "우리" You must not use "우리" implying your superior. At first, you might want to study "우리".
You might forget to mention "tonight" and questions mark "?".
Let's discuss after getting rid of '우리'.
(우리) 치킨 먹을 수 있어요?
'먹다' is not honorific form. However, '있어요?' made this sentence honorific.
(우리) 치킨 드실 수 있으세요? / 오늘 밤 (우리는) 치킨 잡수실 수 있으세요?
Either '들다' and '잡수다' are honorific form of '먹다'. And you can add '시' to make them more polite. So both '드시다' and '잡수시다' are more polite than '들다' and '잡수다'.
오늘밤 치킨 먹을래요?
오늘밤 치킨 드실래요?/잡수실래요?
we commonly omit 'subject' when it is obvious. (Here, everyone knows who is '우리')
In my opinion, '드실 수 있으세요?' is not grammatically good. At least, 드실래요 is much shorter.
No, it's always about whom you're talking to.
If you're talking to a group of elders, then your group of elders (you + older people) would be referred to as 저희. On the other hand, if you were talking to a group of your peers or younger, then you'd use 우리.
So what if you're talking to elders who are part of your group? You use 저희 simply because you're talking to elders.
