Disable parent account sharing Wifi password with child account

In our family group we 2 parents and 2 kids.

Our home network has a Primary Wifi SSID and a Guest SSID.

We want to keep the kids only on the Guest SSID, which we can disable at bedtime.

When we do this, the kids have found that they are prompted on their iOS device to adopt the Primary Wifi from the parents because we are all members of the same Family Sharing group.

How can prevent our parent accounts from sharing the password to the Primary wifi?

We do not want to disable Bluetooth.