Translation:They are my older brother and older sister.
In Taiwan the character "和" is pronounced as "hàn" when meaning "and." Since "和" is frequently used, this difference in pronunciation can be a simple tip to tell the people from mainland China or Taiwan. By the way, unlike Japanese, Chinese characters with multiple pronunciations are in limited numbers, but "和" has 6 pronunciations -- Maybe the character with the most pronunciations in Chinese.
In English (or US English at least) "big brother/sister" is universally understood to mean "older brother/sister," regardless of the siblings' actual relative size. You wouldn't use it in academic writing but in everyday speech and most written English it's totally acceptable.
Sometimes Duo requires the older/younger and sometimes it doesn't when translating to English. As it is required in Mandarin I always translate them into English anyway just to remind myself of the importance of the distinction in Mandarin, even though it is often not necessary in English. It also helps me remember which is which in the Mandarin characters.