1. Jemy wieczorem obiad o god. 7mej. = We have dinner at seven in the evening. [EVERY evening!]
2. Zjemy teraz bigos, kiełbasy i pierogi ze serem i ziemniakami. = We're now having hunter's cabbage, sausage and filled dumplings with cheese and potatoes.
I am sorry Lyzko, but I have few problems with your explanation here. The #1 is not complete because the verb "jemy" may mean two things: the action in the present tense, as well as in the future.
Poczekaj, jemy właśnie obiad, zadzwonię później.
Wait, we are having dinner now, I'll call you later. (Current action, "present continuous")
Jemy obiad w tej restauracji każdego dnia.
We take dinner in this restaurant every day. (Repetitive action)
But being at it, I'll add few more "imperfective" forms, outside your example #1:
Jadamy u Havelka od czasu do czasu.
We take dinnner at Havelek's restaurant from time to time. (Occasional, yet still repetitive action.)
Dzisiaj będziemy jeść obiad raczej późno.
We will have our dinner rather late tonight. (One time future action - but no promise to finish the dinner)
Od dzisiaj będziemy jadać w tej stołówce.
From now on we will be having meals in this cantina. (Repetetive, future)
Your second example cannot be interpreted as something taking place in in the present. The "perfective" (dokonane) actions can only refer either to the past or to the future.
So your #2 example, has two problems - both Polish and English.
Polish: Zjemy (zaraz, wkrótce) bigos, kiełbasę oraz pierogi z serem i ziemniakami.
You could use "zaraz" or "wkrótce" but - strictly speaking - not "teraz". "Teraz" (now) signifies present, "wkrótce" and "zaraz" (soon) are in the future. I guess you could use "teraz" to signify very near future, but such form is not 100% correct.
I am not sure about English translation of this sentence, but this will probably do:
English: We will (soon) have hunter's stew, sausage and dumplings with cheese and potatoes.
So it is definitely a future action, not present.
However, I am not sure how to stress its perfective aspect in English, without adding some supportive sentence, like this:
"After having dinner we will go to the movies." Here the aspect is obvious, since we declare our intention of finishing the dinner first.