Translation:The sister is in the city, the mother is at home.
It should accept ‘Sister is in town, mother is at home.’ While generally English does not hide pronoums, in this case it can, in order to refer to a particular set of mother and sister.
Because the standard syntax in Latin is SOV (Subject, Object, Verb), but Soror est in urbe should also be right, because the Latin syntax is very flexible.
Maybe they translate "town" with "opiddum"?
I don't think that the English sentence should be displayed with a comma splice. I think the translation requires perhaps a semicolon or a conjunction. Just trying to help.
Please, use the "report" button on the exercice page. Because here, we can't see your sentence.
No me admite el posesivo. Los posesivos de familiares directos se ponen en latín para indicar énfasis.
There's no possesive in the English sentence. There's a sister, but we don't know if it's yours. It can be the sister of someone you previously talked about.
John and his sister are at school. The sister got a bad mark.