Translation:Where are you going to go on the weekend?
i think it's acceptable to say "i'm going grocery shopping on the weekend", but not "i'm going grocery shopping for the weekend" (which sounds like you're buying groceries to consume that weekend). you could say, "we're going away for the weekend" but it means for the duration of, in other words, the whole weekend.
At 50+, i don't recall hearing on the weekend so it might be a regional thing. (Or it could just be because I'm 50+ and remember less everyday.) This weekend or for the weekend is natural but on the weekend sounds like im placing something on top of another item. Yes, on Saturday or on Sunday I'm going to .... or talking about an event being on the weekend in the past. The bike ride was ... no then i want to say this past weekend. Just don't think i would use on the weekend. But then I'm no scholar either.
In the US on the weekend and for the weekend would be two separate concepts. "On" would be something to take place anytime during that particular weekend, such as a chore that you've so far put off from doing, while "for" would mean something that knowingly will take up the entire weekend, such as a vacation.
As a literal translation yes, but what you need to know is that the article el or los, depending, is used when talking about specific days of the week. It is the context that tells you to which day is being referred. Por ejemplo: El domingo voy a una fiesta = This Sunday I am going to a a party. Otro ejemplo: El sabado estuve con Luisa = Last Saturday I was with Luisa. In addition to this when talking about habitual actions we use los + day of the week. Por ejemplo: Los miércoles tengo clases de español. = On Wednesdays I have Spanish classes. Otro ejemplo: Mariano trajaba los domingos. = Mariano works on Sundays. I hope this helps.
It's a bit more complicated than that. This explains why "adónde" is correct and "a donde" isn't. https://www.thoughtco.com/using-donde-and-related-terms-3080301
"Van" is plural for both you plural, "ustedes" (you all, or y'all if you speak Southern) and also plural for they (ellos/ellas). "Van" means y'all or they are going (present tense) now. "Van a" means y'all or they are going to do something in the future: Manaña voy a ir al supermercado. Tomorrow I am going to the grocery store.
You may not be looking at the "Tips" in the lower left corner of the page where you click on a lesson. Those tips can be very helpful. Each time I start a new group of lessons, I copy the tips into a computer file for future reference. For me, it really helps.
Either "a dónde" or "adónde" should be accepted. I suspect you have a translation error somewhere else in your sentence, and Duolingo is just giving you an alternative to "a dónde". When we have translation errors, Duolingo consistently suggests alternatives to words we use (suggesting esposo for marido). It can be frustrating because, until we figure it out, we think the word being suggested is the error. Not so. If you think about it, those suggestions, even though frustrating, can help us to learn. When we recognize that, the suggestions, magically, become less frustrating. : )) Hope this helps.
I disagree, I have never used the phrase "at the weekend", but always "on the weekend". It could be a locale thing, I'm in Australia. Ustedes is not used as the verb to go, it is used to indicate that the conjugated form van applies to you all and not them. "Adónde van a ir el fin de semana" could be "Where are they going to go..." or "Where are you all going to go...." so "van a ir ustedes" removes the ambiguity.