Are the set-top boxes connected to all the TVs?
To connect the console to the TV, you need that would match the connectors. These can be RCA or SCART connectors typical of older TVs, as well as modern HDMI. If you don't have the right connector, you can use an extra adapter.
What will this connection give for you?
TV set-top boxes are designed for different types of TVs. The main thing is to check the connectors that would match. Even if you don't match you'll be able to pick up adapters. There are android tv box accessories https://www.infomir.eu/eng/products/accessories/. With these accessories, you can connect your set-top box to the TV.
There are different kinds of set-top boxes and I don't know which one is the best. But I know the site switchonshop and there are several good models. You can have a look at them, read the information and choose what you like. I think the instruction is easy, now it is your turn to make decisions.