Every year I go to my grandmother's house for Christmas and Summer break. My parents are pretty sure that they will give me an Xbox One for Christmas this year. My grandma only has 2 TVs in her house though. One CRT, and another flatscreen. I am not allowed to put consoles on the flatscreen because people use it for watching TV. So I have heard that you should use an HDMI to AV converter, but I wanted to know if I could just use my old Xbox 360 AV cord on the One.
No, the Xbox One does not support the AV cables used with the Xbox 360. The only output featured is for HDMI.
For connecting an Xbox One to a TV that only has the older AV ports, rather then HDMI input, your best bet is to use a HDMI cable with a HDMI to AVI converter. You can generally find these at an electrical wholesaler, although electric retailers will likely have a similar solution, too.