"Tomorrow we are going to go to my sister's house."
Translation:Morgen werden wir zum Haus meiner Schwester gehen.
Let me try to address the words "nach Hause" which are referred to in several queries and, while I'm at it "zu Hause". I'm pretty sure that they always refer to the home of the subject. If I say "Ich gehe nach Hause" that's going to my home. That can't refer to my sister's house (unless she lives the same place I do - not unusual, but not what seems to be referred to here). If I say "Meine Schwester geht nach Hause." then that's referring to her home.
Similarly, if I say "Ich bin zu Hause." That means I'm in my own home. If Dan is visiting me and sitting next to me, I can't say "Dan ist zu Hause." That would imply he is in his own home, not mine.
First: 'go to' = 'gehen zu', you're missing the 'zu'. Second: syntax. Toss around some words and get: 'Morgen gehen wir zu meiner Schwester nach Hause' and you get a rather colloquial sentence, in my opinion. It would translate to 'Tomorrow we are going to visit my sister at her home'. I don't like the german translation given by duo here, since it translates to 'Tomorrow we're going to my sister's house, stand around outside and won't even ring the bell'. That might be intentional, but misleading anyway.
Tough one. I've typed an answer but scrapped it. Anyway, I've found this great explanation for you: http://german.about.com/library/weekly/aa061900a.htm
Aha! You've discovered one of the great German Learning Headaches(GLH): Depending on the location you can use nach, zu, or in! (Wir gehen ins Kino). I have yet to come across a really clear table detailing where one uses which preposition and have just decided to learn by individual example . . one does end up getting an ear for which sounds 'right'.
OK, so I thought I had the whole dative/accusative case thing sorted out with respect to prepositional phrases, but apparently not. In this sentence, the dative case is used for "zu dem Haus." However, I thought that you would use the accusative "zu das Haus" here because there is movement/change of state. We are going to the house, we are not in the house. Somebody help, please!
The action/inaction rule only applies to the prepositions that can take EITHER the accusative or the dative. There are some prepositions that always take the accusative, some that always take the dative and then don't forget the few that always take the genitive! (I can only remember anstatt, während and wegen at the moment). Ah, the joys of learning German – it certainly keeps you on your toes :-)
"Gehen" implies walking. "Fahren" implies "going" in some sort of vehicle. So if it is farther than you would walk, then you use "fahren". The big joke in Germany is when someone says, "Wir gehen nach Amerika." and people say, "Ziemlich weit zum gehen..." HAHAHAHA!!!! (well... it's not THAT funny, but anyway.)
You CAN put Morgen just before gehen, but then you MUST have a subject. eg. Morgen gehen wir nach Hause. In a statement, the verb MUST come in the second position and the subject must be attached to it. You can begin the sentence with any number of things: Subject, Time expressions, Objects, Adverbs, Locations. This acts to emphasize the first word. The Usual structure however is Subject then Verb then modifiers.
Construction wise, it isn't wrong, but the convention is that you tend to put the time expression earlier in the sentence. The general rule is: Subject, Time expression, Objects, Manner (adverbs), Place. Which spells STOMP. You can put any one of these expressions first, but then the order changes, but keep the rest of the expressions in the original order. For example: P then STOM or O STMP
Remember, Duolingo doesn't have EVERY correct possibility listed. If you think it should be right, let duolingo know.