A:AnswerThis is a router, not a modem. The modem is what the coax cable plugs into - it feeds the router, which is the device that creates a WiFi network. If all you have is this device, you still need a modem.
A:AnswerI have links maxstream ac2200. Its a little pricey around 200 but it works great and has a on off switch on the back to cut the kids wifi at night time.
A:AnswerIt depends upon how far away the house is in relation to where you set up the router. This router does have very good range, but if signal is weak you could purchase a range extender and put that in Grandmas house to boost the signal from your router