internet

If that is a Sony audio/video receiver and it has an Ethernet port or is WIFI enabled that could be connected to the gateway. IF the receiver has no network capability then it is of little use for this.

The main part is having a device that can run/host the steaming applications. An AV receiver may be able to have multiple devices connected to it but if those devices do not run the streaming applications say Netflix or Amazon Prime Video, or Paramount+ etc… then it would not really help much. 

The best and simple solution would be to get a TV that has the "smart TV" capability. I have a Sony Wegagate vintage 60" TV which is NOT a "smart TV". I send the digital delivery to it from one of several internet capable devices that do have the applications that allow us to see the programming. It is not a difficult solution to set up but my components are not old, other than the TV itself. I have been asked why I still run the large older TV but I only care about 1080p resolution so it works for me. Sure a newer 4K TV might be nice to have but it is not a necessity to me. When this fails I will replace it. My gear is getting older so it does limit some of my options but that is not important to me.

The capability of the components in the solution is important. It would take more work and time to sort out what you have and know if it could provide a solution. Again the simple fix, if you are not technical or do not have access to someone that is would be to buy a smart TV. You could still use your old TVs for reception with the antenna you have for that programming. A newer smart TV would open up more options for programming. If you bought a smart TV from Best Buy for instance, you could have them deliver it and set it up for you and you would be all set. If you are not technical this is a great way to get it done and use the gateway for steaming and basic browsing etc…

If you know the model numbers for the TVs and receiver that is easy to look up. If you don't have any devices that can run the streaming applications for viewing the programming options then that is what you would need to have to get started. You can use a computer to do streaming. Getting the service to one of the TVs is another challenge.