Minecraft, second account under the same microsoft account (paid)?

My kids want to play Minecraft on two PCs together. I bought a Minecraft account on a PC with my Microsoft account.

How do I get another account on the other PC now? I'm registered there with the same Microsoft account.

I want to pay for the second account too! How and where and with what can I register? In the store with a different Microsoft account (i.e. Create a new one)?

No unfortunately not possible!
You would have to create a separate account and buy Minecraft there once.
Unfortunately you can't play twice at the same time with the same account!

As far as I know, the Bedrock license (in contrast to the Java edition) is not bound to an account. So you can simply log in with a different MS account within the Minecraft you have already purchased. You don't have to buy it again if you are logged in to both stores with the same Windows Live ID. Buying again would of course also be possible. To do this, you would have to log into the store with a different account. But the login within the game does not have to be done with the same MS account as the purchase, so buying again would not make sense.