Multiplayer Minecraft

Hi,

I have set up a Microsoft account that I used to purchase Minecraft with on the xbox and then again my daughters MacBook, now that they are playing on Java my daughters can't play together so they are wanting to play together on their laptops. I do not want to have to buy the game a 3rd time when we all live in the same house. Is it possible for the 2 girls to play together without having to buy the game again for a 3 device? They would both be playing on Mac books. I have set my daughter up with her own Microsoft account under my account name as a family member, but when she try to use it to sign into Minecraft it says she must pay for it. I have had my daughter try to Set up a host word and open a LAN for my daughter to join but it also says it's unable to join. Any help would be so greatly appreciated. I have been trying to troubleshoot this for over 4 hours. Thank-you so much