Pension and URSSAF contributions as an auto-entrepreneur?

I am an early retiree, in receipt of a pension from the UK and wish to start working again as a sub contractor for my brothers company. We have lived here 6 years, have Carte Vitales issued by CPAM and pay URSSAF quarterly. I also pay Hotel d’Impot annually on my pension which is paid in the UK. I have a couple of questions which I would like your help with please.

If I opt for the auto-entrepreneur scheme, what happens regarding the payments we currently make to URSSAF once I have set up as an auto-entrepreneur and start paying the cotisations. It is important for us that cover continues uninterrupted as my wife has an illness of long duree and receives the appropriate cover for it. What I don’t want to do is pay twice for the same thing but having said that, I appreciate that the amount we pay is based on my existing pension and not on future additional earnings.

The work I intend to do is seasonal and a service. I will invoice customers on my brothers EURL to include TVA and receive an amount back from him as my income. My turnover will be less than 32,000 euros per annum and my outgoings will be mainly to cover my car running expenses and petrol. From what I have read, I think that the auto-entrepreneur scheme is the most appropriate but would like your opinion please to ensure I am on the right track. Any help you are able to give me will be most appreciated.