waterfox or firefox, new brave browser could be nice, but i haven’t used it much.
for grandma probs firefox sadly.
ublock origins, httpseverywhere, duckduckgo plus and youtube enhancer.
as much as i wish one could do it, one can’t install noscript on a normie computer.
so definitely one addon, that blocks major trackers from facebook and google, as noscript is not an option for them, but a perfect one doesn’t come to mind.
and with duckduckgo plus and duckduckgo setup as primary search option, learn them a few “bashes”, which will make it easier for them to search on youtube (… !yt) or other sides directly from the browser search bar.
and i’d setup darkmode on youtube and duckduckgo for them probs and show them the option to disable or enable it.