Final answer:
The correction needed for the given sentence is to change 'twins' to the possessive form 'twins'' because the house belongs to the twins.
Step-by-step explanation:
The revision that should be made to the sentence: 'Santa's first stop last year was at the twins house on Elm Street in Allerton, Iowa.' is option a) Change "twins" to "twins'". Since the house belongs to the twins, the possessive form should be used, which is twins'. None of the other revisions are appropriate as the original sentence does not require changes to "Santa's", there is no need to delete the comma after "Allerton", and there is no need for an additional comma after "house".