Translation:They want to take a taxi to our house.
lol I guess they're trying to push the learning outcome that 坐 can mean to be a passenger of a vehicle, so they're looking for some evidence that you've picked up on that. With that in mind, I think "use" is correct, but not the best possible translation of what they wrote.
Yes, though this is definitely a regionalism. 德士 (dak1 si6-2) is a Cantonese loanword for English "taxi"; Wiktionary says that it is used in Malaysia and Singapore.
I know from personal experience that the very closely related 的士 (dik1 si6-2) is used in Hong Kong and Macau.
I'm not aware of any places where Mandarin is the primary Chinese language where they use these terms, but happy to be corrected.