1. The two of them went to the store to get her a birthday gift. Die beiden/zwei gingen in den Laden, um ihr ein Geschenk zu besorgen/kaufen. It works like an abbreviation of "die beiden/zwei/drei/vier/fünf/... Männer/Frauen/Personen/...": "die beiden/zwei/drei/vier/fünf/..." die + [amount] 2. The two of us want to study Irish. Wir beide/zwei wollen Irish lernen. You can say "wir + [amount]": wir drei, wir vier, wir fünf – as long as the quantity stays manageable. "Wir zwanzig (20)" sounds a bit strange. "Beide(n)" is often used instead of "two" when one is refering to certain people – not any people. You have to use it with the definite article. die beiden Männer, die beiden Kinder, etc.