"We will get married."
Translation:Vi ska gifta oss.
In the incubator it looks like this sentence is taught in Future, Lesson 2, which seems reasonable. Where did you get it?
Yes, Vi skall gifta oss is OK too. skall is a bit formal so you run the risk of not having it accepted just because it hasn't been added yet (I added it here now). I'd recommend writing ska in all sorts of texts though (even formal ones).