Keep connecting to 5GHz network despite disabling 5GHz SSID broadcast

I don't have any Apple products, so take this with a grain of salt, but you may be able to block your computers (and maybe phones) from connecting to certain wireless networks via MAC addresses. The router and satellite should each have a unique MAC address for 5GHz and 2.4GHz (plus one for each ethernet LAN or WAN interface). So, for instance, the RBR50 should have like seven MAC addresses: 1x ethernet WAN, 3x ethernet LAN, 3x WiFi (since it's triband; 1x 2.4GHz, and 2x 5GHz (one for devices, and one for the backhaul to your satellite(s)). The RBS50 should be basically the same, except 0x ethernet WAN interfaces, and 4x ethernet LAN interfaces.

You may be able to go into your network settings on your computer and basically blacklist the router's and/or satellite's 5GHz MAC address(es), which should then force it to connect only to the 2.4GHz radio instead. This is probably easier to do on a computer than a phone, and may be impossible to do on any smart IoT devices you can't operate on directly (e.g., smart speakers, wireless speakers, etc., that require configuration through an app or website). But, in theory, any device with advanced network configuration settings where you can block APs should allow you to force it to connect to one radio or the other by blocking the one you don't want it to use, thus forcing it to use the other.

You'll have to figure out the MAC addresses for the router and satellite(s) for the bands you want to block, and figure out how to configure each device you want to specify the band it uses.