Not stupid at all! It seems that in Turkish, since there is one verb that means both do and make, you differentiate the meanings using either için, or the dative case.
Onlar için yapmak - do for them
Onlara yapmak - make for them
But this leaves me wondering, how do you say "to do to them"?
'Ne' in this question is indefinite direct object and indefinite direct objects must come before the verb. But if it was a definite direct object instead its position could change. For example:
Neyi onlar için yapabilirsin?
But the neutral order is given one, this would most likely be used for emphasis. However, i should warn you that predicate must come at the end in this sentence.