increasing icloud storage, sharing storage, and an unnecessary icloud account
I have an icloud account which I share with family members. I recently got a message saying that the account was full and suggesting I upgrade to 2TB. Three other family members are connected with the account and each of them share my current 2GB storage. However, for some reason I realise I am also paying for a separate account for one of these family members - my son. It is also a 2GB storage account. If I upgrade the main account to 2TB, can I stop paying for the extra account, since my son is already set up to share my icloud storage? As I said I have been granting him access to my own icloud storage all this time even though I am paying for a separate account for him. I would like to pay one amount for the whole family. But I also do not want to lose any data from my son's account. I don't know how I managed to mess things up like this. Can I go ahead and increase the family icloud storage on my phone and then tell him to downgrade his icloud account without any risk to his data? By the way, he is now 19 years old and I don't know if this makes a difference to family sharing. Any help would be greatly appreciated.
iPhone XS