How to make a organized and safe home computer network?

Question

Hello I am a father of 2 children and I live with my wife. As the kids are growing up, I need to buy them computers and smartphones. In order to make my house network organized, efficient and safe, my idea is:

1. to create in each computer of the house accounts for each family member so that everyone can use them.
2. share the data of a specific account to another PCs with the same account. In other words , the data should be synchronized preferably though the in-house network without using cloud services such as OneDrive, Google Drive... (when/if possible). Maybe NAS?
3. the main administrators (my wife and I) should be able to access all the PCs and the data of all accounts.
4. replicate point 1. 2. and 3. for Windows and Ubuntu OS as all devices should have double partition.
5. block to all devices from specific websites not suitable for children (this operation should be done by the administrator and propagated automatically to all users.)
6. Repeat point 5. to all tablets and smartphones running Android or iOS devices

I would like to ask therefore if you can suggest me the practical steps that i need to take in order to achieve turn this task into reality. Of course you can suggest me also some guidelines either through your experience or tutorials or projects where I could start from.

Note: feel free to propose suggestions or other ideas to improve my project.