"Who are going there to the turtle?"
Translation:Kik mennek oda a teknőshöz?
1) "Kik odamennek a teknőshöz?" should be accepted, I think; I've already reported it.
2) "Who is" sounds more natural. I'm pretty sure who is always conjugated in the singular unless it refers to something else in the sentence that's explicitly plural, such as in "Who are the actors in the movie?" Otherwise, even though the plural "actors" is implied, it's not explicitly stated, and we would just say "Who is in the movie?"
I agree with what you say in (2) but I think the question in (1) really wants to have the interrogative kik right next to the verb stem mennek.
That's correct on (1), the verb needs to be split up:
"Kik mennek oda...."
Maybe we can establish this rule: if the emphasis is on the subject as in this sentence, then the preverb is most probably separated.
It is probably true in a more generalized version: if the emphasis is not on the verb, then the preverb is usually separated.