Questions & Answers about Мама и сестра дома?
How do we know this is a question if the word order is exactly the same as a normal sentence?
In Russian, you form a yes/no question simply by changing your intonation. You raise your pitch on the key word you are asking about (here, дома) and drop it at the very end. The written words are identical to the statement for "Mom and sister are at home."
Where is the word for "are" in this sentence?
Russian drops the verb "to be" (am, is, are) in the present tense. You literally just say "Mom and sister at home." You only need a word for "to be" when talking about the past or the future.
Why is the word for home дома instead of just дом?
The word дом is a noun meaning "a house" or "a building." The word дома means "at home" or "in the house." You use дома when talking about a location, like where someone currently is.
How would I answer this yes/no question?
You can answer simply with Да (Yes) or Нет (No). If you want to be more specific, you can say Да, дома (Yes, they are at home) or Нет, не дома (No, they are not at home).