This information is 100% incorrect.
I know you're just trying to help, but answering a question when you're not sure of the answer can 100% be devastating for the person asking for the help. In this case, there are three options: They fly here in May before their visas expire and stay for good, they fly here and activate their visas, return home and come back permanently in September, or they allow their visas to expire and then they'll have to start from the very beginning again.