UC migration from ESA Support Appointee ID issue

Hi, I am my son's appointee. I received the migration letter to move him from ESA support group to UC. I filled in the online form and provided details of two forms of his ID. They haven't accepted that and have made an appointment at the local job centre on Monday. It is impossible for my son to attend or to be interviewed at home. It is also difficult for me to attend. Whose ID do they need, his or mine? I had been under the impression that neither of us would have to attend any interviews.

I would be grateful for any advice, thank you