Running a game for a group who have never played

Hi all, I'm running a one-shot soon for my family. The group will consist of my uncle and his son (avid players), my partner (who has played before), and my mother and grandmother, both of whom have never played. I want to make it as easy as possible for the newbies while still being fun for the experienced players. Does anyone have any tips?

I think I'm gonna strip it way back, decide everyone's characters for them (while my uncle, cousin and partner could design my own, my nan can barely use Facebook let alone D&D beyond), and ensure a good range so that everyone can play at least a little bit. I'm struggling with a structure for a one-shot, but I think I'm gonna consult the arcane texts (watch some one shots online and steal one of those)