eons ago I heard and internalised an awesome phrase: “don’t analyze the problem - solve it”.
in that vein, install it yourself and ship the laptop to him. don’t matter what it cost, it’s not like it’s gonna bankrupt you and it’s not like you’re gonna do this multiple times per year.
you’re 100% in control of everything and that’s the next best thing to being there and doing it for yourself. you’re gonna figure out how to remotely do half of the things you mention across CGNATs and whatnot? I am sure you got better things to do; I know dad has.
kodi and its derivatives are not something you should be using. it’s shit software on so many levels and we should burn it in the deepest volcanos we got.
try one of these:
run lineageOS TV (konstakang images) on it and install regular ATV apps for the services mentioned. so, like googletv except there’s no spying and ads and shit.
create a normal linux box that has a DLNA sink e.g. using macast. there’s no remote control, you use your android/iOS device to send it stuff, like movie from Jellyfin or a youtube video, and it plays it back and allows some control (pause, play, rew/ff, etc)
dedicated Jellyfin box; same as 2) but boots right into jellyfin client. it can be run in TV mode where it reacts to only up/down/left/right/enter/back, via gamepad or remote controller. if yours isn’t recognised, you can emulate it with InputRemapper.
not familiar with how twitch does stuff.
you also have the option of installing a normal raspi distro and then using a wireless keyboard and mouse/touchpad to run it, but I am of the opinion that once the device gets placed by the TV, it loses all keyboard and mouse privileges and should only be operated via the TV’s remote.