Hi, I am Dave, I will help you with this.
When you remove the children from the Microsoft Family, they will then become administrator on their accounts like normal adults, they would not require any permissions any longer from an adult.
With regards to the Microsoft 365 (Office) Family account, it depends on the method used to install Office for the children, did you use the Share option provided on the link below to give the children access to Office on their own accounts with their own Microsoft Account logins and 1TB of OneDrive storage?