TeamViewer works well for my family. However for security reasons I have configured it to not be always on. So I instruct family members to launch it only when

TeamViewer works well for my family. However for security reasons I have configured it to not be always on. So I instruct family members to launch it only when they need my help and send me over their ID and passcode. Another option is Chrome Remote Desktop but I haven’t used it in years. Also for safety I recommend putting the sibling on a non-admin account. This way there is limited damage they can do. While Mac OS does have built in Remote Desktop capability you would need to setup access to the network the laptop is on. And you wouldn’t want to expose that server over the net.