Learn Hardcore Korean: urineun babeul meokgo isseoyo.

우리가 uses the subject particle -가, which emphasizes “we” as the subject performing an action (less topical focus).
Just 우리 without a particle is incomplete in Korean unless context or a following particle (like a possessive 의) clarifies its role.
In this sentence, the speaker wants to talk about “what we are doing,” so 우리는 (as topic) is most natural.

What does 밥을 mean, and why the -을?

밥 literally means “rice,” but in everyday Korean it often means “meal.”
The particle -을 is the object marker attached to nouns ending in a consonant. It tells us that 밥 is the direct object of the verb 먹다 (to eat).
So 밥을 먹다 = “to eat (a) meal/rice.”

What’s the function of -고 있어요 in 먹고 있어요?

-고 있어요 is a present progressive construction equivalent to English “-ing.”
You form it by: verb stem + -고 + 있다 (conjugated politely as 있어요).
Thus 먹고 있어요 = “(I/We) am/are eating (right now).”

How is 먹고 있어요 different from 먹어요?

먹어요 is the simple present: “(I/We) eat” or “(I/We) will eat.”
먹고 있어요 emphasizes an action in progress: “(I/We) am/are eating (at this moment).”
Use -고 있어요 when you want to highlight that the action is happening right now.

What level of politeness is 먹고 있어요?

-어요/아요 endings denote the polite (but not overly formal) speech level, suitable for strangers, co-workers, or people slightly older than you.
먹고 있어요 is polite but friendly—common in everyday conversation.

Can the subject 우리는 be omitted?

Yes. Korean often drops the topic/subject when it’s clear from context. So you can simply say 밥을 먹고 있어요 if it’s obvious you’re talking about yourselves. Including 우리는 adds emphasis or clarity.

Could I use 계세요 instead of 있어요 for extra politeness?

Yes. -고 계세요 is the honorific progressive form, showing respect to the subject. Use it if you’re talking about someone senior or you want to sound more formal:
“(어머니께서) 밥을 드시고 계세요.” (Mom is eating.)
But for “we,” -고 있어요 is appropriate—you don’t need the honorific form for your own group.