Sentence 1: It was almost Halloween and they didn't know what they'd be. 
 Sentence 3: They looked online to get ideas for couples 
 Sentence 4:  They eventually decided on something they thought would work 
 Sentence 5:  They decided they would be Mary Poppins and Bert 
 Option 1: They went to the store to look at costumes. 
 Option 2: They went to the store, and bought costumes.