Let me add some information. (1) 私たち → the most common word to say "we". Could be two or more. (2) 俺たち → very casual. Really masculine. Could be two or more. (3) 僕たち → casual. Kinda masculine but Tom boy girls recently use this (manga influence). Could be two or more (4) 我々 → SUPER formal. Really bossy. Could be two or more (5) 我等 → extinct word. No one use this. Could be two or more (6) 自分等 → kinda slangy. Kinda masculine. Could be two or more

Not only for 2 people. I think in daily conversation just use 私たち , because 俺たちsounds masculine, informal, and is only used to speak with the same age person or with a person really close with. I only found われわれ in a newspaper, so it seems that word too formal and rigid.

As Fiewfiew said, we use 私達 in everyday conversation. It's as same as WE in English, you can use it for MORE THAN TWO PEOPLE including "I". Ex.) we, the Japanese people, my classmate and I, my sister and I, my son and I, etc, all kind of WE is 私達.