You do say this in English (I'm American). But you wouldn't say it if you were going to their house. Rather, if someone said "are grandma and grandpa coming to us"? You would say "no we are going to grandma and grandpa".
It is more uncommon, but not unheard of. It depends on context and without context you'd assume they mean their house in the sentence above--sometimes duolingo does such sentences. ---ie. Pardon ik ben een appel.
A more clear sentence would be, "we are going to grandma and grandpa's house."
It depends. You could already be at Grandpa's house and jump out of the car and tell mom and dad that you are going to grandma and grandpa or you could be at your own house and grandma and grandpa have just arrived and you are going to greet them, or they could simply be in another room.
My Dutch wife confirms that this is what you say when you are going to visit oma and opa at their house.. so lets admit that that is what this means and forget other scenarios. In Dutch you say you are going to the person but in English you say you are going to the place that belongs to them, their house is their possession. So the correct English must have the s at the end. We are going to grandma and grandpa's (house). Please just admit that this is wrong and correct it.
It actually is a fairly good reason. They have to put every single optional translation in by hand. If they did every minor usage, that would be a lot of work, and it would slow down the path to beta and then full release considerably. This is true of all the languages. The German tree doesn't accept "nanny" or "nana" either, as far as I know. There are simply too many words in the English language to include every possible translation ever.
Thank you, I see that you understand my argument, and I understand and accept yours. By the way, I realise that obviously not every alternate translation could be noted before the beta release of the course. I did not necessarily expect 'nana (etc.)' to be accepted, I just think it should be. I suppose that's really the point of the beta phase - fix up mistakes, and make the course more user-friendly to everyone. Grazzi ħafna.
I still have to disagree. One or two extra alternate translates cannot possibly slow down the entire course. And when it comes down to it, 'nana' and 'nanny' are both very commonly used terms and should definitely be accepted.
And besides, what is the 'Report' button for? It is so alternate translations and mistakes can be brought to the course-makers' attention. 'Nana / nanny' are just as valid alternate translations for this sentence as any other translations for any other sentences.
Your disagreement is duly noted, but economies of time disagree with you--the more things you have to do (there are many sentences with grandma or other words that people want accepted) the more time it takes to release a product. They would have to do all the sentences with "grandma" plus any others that have alternate meanings that people report--you can see that this could get out of hand quickly.
As far as 'nana' and 'nanny' being very common, I never hear them in the western or eastern United States, (I think it's a southern thing)? It's VERY regional.
However, I agree with you that if you report it and they accept it, then great! However, for the time being, it might be safer to use the standard "grandma".
This in English is fine. It seems strange only without context. "Who do you ask about forestry?" "I go to grandpa and/or grandma."
But more importantly, in Dutch when you go to (someone), you go to their location.
Naar is to but try to think of it as being synonymous with 'near'. I go near grandpa and grandma, where 'near' means into their vicinity.