"When are you going to ask them about their vacation?"
Translation:¿Cuándo les vas a preguntar sobre las vacaciones?
When referring to things directly connected with a person, the definite article rather then the possessive adjective is most often used by the Spanish e.g. "Lavamos los manos" for we wash our hands. Presumably on the basis that we are unlikely to be washing someone else's hands in the normal course of events.
I entirely understand this with regard to hands, especially since the verb is often reflexive. But why on earth for "vacaciones"?! It could be for future vacations together or vacations the speaker is taking with the one spoken to and tries to get information etc, etc.
What is wrong with adding the personal pronoun "tù". It is accepted in other similar cases?
I was incorrect with "cuando tu les vas a preguntar sobre sus vacaciones" It looks like Duo now accepts "sus" so why is having the "tu" incorrect?
isn't it okay to say "cuando vas a preguntarles sobre las vacaciones" and attach the "les" to "preguntar"
PLEASE EXPLAIN WHY THIS IS WRONG: "Cuando tu les vas a preguntar sobre las vacaciones."
I'm used to being very formal, so I used "va" instead of "vas." Why is this incorrect?
The question itself seems more informal to me than formal. After all, would you walk up to your boss, your teacher, or someone that you don't know very well and ask, "When are you going to ask them about their vacation?" That could be blunt in some cases and rude in others.
Why does the les go in front of vas instead of preguntar when I'm asking them?
Cuándo les vas a preguntar sobre sus vacaciones a ellos? What is wrong with this?
You got the main sentence right, however, "a ellos" = "to them" is not needed.
¿Cuándo vas a preguntarles sobre sus vacaciones?
"Preguntarles" already clearly says "to ask them", and "sus vacaciones" establishes the fact that it is "their vacation".