As the comments by Jon Hanna and Araucaria (above) indicate, the three examples you give are not faulty as a matter of parallelism or grammar. But the example sentences you provide don't consist only of "A helps B to Verb1 and helps C to Verb2," "A helps B to Verb1 and C to Verb2," and "A helps B Verb1 and C Verb2." Rather, because the verbs involved are transitive, they introduce direct objects of both Verb1 and Verb2:
"A helps B to TransitiveVerb1 ObjectC and helps D to TransitiveVerb2 ObjectE."
"A helps B to TransitiveVerb1 ObjectC and D to TransitiveVerb2 ObjectE."
"A helps B TransitiveVerb1 ObjectC and D TransitiveVerb2 ObjectE."
where ObjectC and ObjectE are the objects of TransitiveVerb1 and TransitiveVerb2, respectively. Unfortunately, these additions to the logic of each sentence complicate the task of associating the parts properly, especially at the "ObjectC and D" point of the second and third sentences.
At the very last, I would add a comma after ObjectC in the second and third sentences, to indicate a break where the break from one parallel branch to the other occurs. Even then, I think the first sentence of the three is clearer than the other two.
And finally, for reasons that probably have more to do with idiomatic patterns of usage (or perhaps personal idiosyncrasy) than anything else, I would use a fourth structure, instead of any of the three you offer—namely,
- "A helps B TransitiveVerb1 ObjectC and helps D TransitiveVerb2 ObjectE."
(omitting to twice), which in your original example would translate into this sentence:
"This test will help students find their talents and will help their parents understand those talents."