How to restrict access so that only one machine has access to files and programs?

Question

Computer networks

We have a router and several computers that receive addresses via DHCP. Made a local area network between computers. Home group is everything. There is only one computer in the homegroup that will connect to the remote machine. Do I need to somehow additionally block access so that no one else can hack into the public folder? And in general, how can I secure this network to a minimum?
PS Access to the folder (in the sharing settings) set reading and writing to everyone, not only to those who are at home. Otherwise, I got to my homework, but access to the folder did not open

Answer 1

Give access to the network folder only to the right user.
All the others naturally will not be able to connect.