Have a Tax Question? Ask a Tax Expert
You can pretty much claim what you want on your W4, it's just what you claim will affect what you owed, or are owed, at the end of the year. If you are getting a small refund, then your withholding is spot on. However, if you would prefer a refund, I might suggest you change your W-4's to the higher single rate, or in your case S-2.
If you would like a larger refund next year, then yes, he should switch too.