How do you say "We eight are..." in Japanese?

Answer 1

If you're a guy and you're in a casual situation, you'd usually say　俺ら八人 (Ore-ra hachi-nin) or　俺たち八人 (Ore-tachi hachi-nin)
In a more polite or formal situation, you would probably say 僕たち八人 (boku-tachi hachi-nin)
If you're a female in a casual situation, you could say あたし達八人 (atashi-tachi hachi-nin)
In a more formal setting, 私たち八人 (watashi-tachi hachi-nin)

Answer 2

I'm assuming you are talking about people.

私たち八人は… [ watashi tachi hachi nin wa ...]

Answer 3

我々八人は・・・・・
(Ware ware hachi nin wa)