The DWP have the same right as the claimant - that is, to request a Statement of reasons from the Tribunal Service and take this further only if they can demonstrate that an Error of Law occurred.
What is an Error of Law? Otherwise, the decision must be put into action. Your son does not need to do anything meanwhile.
I have answered another message from you on the same subject. Please keep all messages about this in the same topic, we don't stand a chance of giving accurate information if everything from you is all over the place!