You should be able to just start the 1040X (check the year) and any similar amended State forms.  Then go the "Info" page (where you enter the taxpayer's name, address, SSN and the dependents), and just delete the dependents (right-click, then hit "delete line").

Then that should automatically change the 1040X to show that change.

As a side note, I don't know what your taxpayer's situation is, but MFS and an "attorney" seems to indicate that husband and wife may not be living together.  If your client wants to claim the children in future years, you need to check if he is eligible to claim the kids.  The kids need to have lived with him for over 1/2 of the year (or would have lived with him if the kids are temporarily away at college).  Likewise, the wife can't claim the kids this year unless the kids lived with her.