What error in parallelism is made in the following sentence?
not only vacuuming, but the family wants to dust and straighten up the whole house.

As you can see, the error in parallelism in this sentence is the use of the verbs. The first verb is in the -ing form. Supposed to be, the next verbs should also be in the same verb. But what happens in the next verb is that it uses the to + base form of the verb form. Hope this answers your question.