You can just install minecraft on all three Mac accounts, and set up the same microsoft account on every account. This will prevent them from having their 'own' game on some servers, as the items and things you do on a server are linked to a certain account.

If your kids just want to build some things in singleplayer and have fun doing that, a single microsoft account on all MacOS accounts will work great.

okay - i can’t quite confirm this, as i am not in front of my home computer right now, but if i am wrong, i am certain someone will correct me.

• use the admin account on the computer to install the game for all users, that way no matter what account is logged in, they will have access to the game

• you will need to create a Microsoft account for each kid. best to use your account as the parent account, and have them as users/family members

• if you have Xbox Live Gold, there’s a good chance the game will be free for you.

• you should play too! it’s a ridiculously fun game, and there’s so many different ways to play it.

if i got any details wrong, i apologise. (except for the part where i said you should play too!!!)

If I understand the question right, you have one PC with multiple accounts? Assuming yes, this is not a problem whatsoever, it'll only get weird when you try to run them at the same time.

You can make them have separate singleplayer installations under the same Microsoft account. However, their multiplayer accounts will be the same as it's tied to an account. Minecraft isn't the most expensive, so if they all intend to play multiplayer, I'd recommend getting them separate accounts.

If you have one account on the mac and want three different instances, you can use MultiMC. Or just have them make separate worlds which is probably simpler if they're happy with the same game settings.