Finding a new Appointee

My nephew ( 36) has been on ESA Support Group for 11 years. His Appointee
His Father received a letter a few weeks ago giving a date but no time for a phone interview.

We are not sure what this for.
All the letter says “ to ensure x is receiving the correct amount of ESA”.
Evidence of Bank Statements, savings, etc must be available.
It will be easy to provide all the paper evidence, My nephew has no savings that I am aware of.

Is this a review of his Entitilement to ESA?
He was diagnosed Aspergers Syndrome at 16 and has never worked in his life.
He has flirted with online gambling which we have discouraged, causing much friction with family.

My Nephews half sister who now has LPA for the elderly and unwell father has managed to put off the interview until we can find someone to replace the Father as an Appointee.

The half sister will cancel the role of Adult Appointee for the Father.
Can my Nephews Mother who lives in France take on this role ?
She would willingly come to UK for any interviews, reviews etc if the DWP were willing to communicate with her in France. But she herself is recovering from a health problem and will need a few more months of recovery, before she can travel.
She is British and so language would not be a problem.

My Nephew has always had his ESA and other Benefits paid directly into his own Bank Account. Can this continue if there is a new Appointee ?

My Nephew lives on his own in a rented property managed by Trustees, but they are not Benefit Advisers.
I don’t want to take on an Appointee role, it would cause friction with my Nephew and I usually spend 5 months per year in Cape Town ( my home city ).

I believe there are commercial organisations that take on The Appointee Role.
Can you advice are they reliable and competent.?