"Where in China do you all live?"
你们 (Nǐmen) = You (Plural)
住 (zhù) = To live
在 (zài) = in
中国 (zhōngguó) = China
哪儿？(nǎ'er?) = Where
Nǐmen zhù zài zhōngguó nǎ'er? = Where do you(all) live in China?
住 is the common verb for "to live". Otherwise, without 住, the sentence then demonstrates
Where in China are you?
I put '你们都住在中国哪儿' because I saw that 都 means that everybody is included, so why is it incorrect?