Greg has to extend his Wi-Fi in order to stream to the TVs around the house. What kind of extender should he get? Leo says the farther he is away, the less signal and speed he'll get. So he'll need to boost the signal. If he's using a modern Wi-Fi router that uses 802.11AC, then it'll be easier. But if he has to use a router provided by the cable company, he should try and see if he can put the router/modem in bridge mode and use his own router. Then he should turn off the modem's Wi-Fi radio as well.
Leo also recommends upgrading to a mesh router, like the Netgear Orbi, Eero, Plume, or Velop. They are designed for challenging Wi-Fi environments by having a base unit with additional plug-in units he can put throughout the house. This essentially creates a mesh of Wi-Fi access. He'll need one plug-in unit for every 1000 sq feet, but they aren't cheap. Base units are $300, and more plugin units are about $100-150.