Technology

You can disable Edge if you don't want people launching it... "accidentally." There are a myriad of ways. Most recently I've used Edge Blocker, which does what it says on the label. Note that this will cause the opening of any file types associated with Edge by default to silently fail if you don't reassign them to some other program.

The install Firefox and uBlock origin. Unless your parents deliberately go out of their way to download and install Chrome (and depending how heavy-handed you want to get you could even prevent this by busting them down to a limited user account) they won't have any choice but to use the correct browser installed on their system. That is to say, the only one.

Beside a big whack behind the head, Ublock Origin Lite is supported on chrome. You lose some features, and it is slower to update, but should still mostly work. Unfortunately, the youtube/ublock fight move quite fast, so results won't be as good on that front.

If they are technologically inept, reduce their accounts to limited, lock down the admin account. That will prevent them from uninstalling FF/installing Chrome, and if the admin account sets a shortcut on their desktop(s), they won't be able to remove it. Disable Edge (there are multiple ways to do so), install the necessary extensions on FF, then change FF's desktop icon and text to "Chrome".

Problem solved.

Change default browser to Firefox

Change file type associations

Setup a firewall and black access to websites where they're able to download other browsers. Then change the icon for Firefox to Chrome's icon. For bonus points, you can probably find a firefox theme to make it look more like chrome.