Hello alon alon elijah,
Welcome to Microsoft Q&A forum.
As of now, there is no official way to share a game on PC via Microsoft family group. Microsoft does offer game sharing; however it only works on Xbox via Home Console function.
There is a workaround for this that you could try. If you are using a child account of the family group, you can sign in with the parent account that own the game to the computer first and then sign in and play with the child account. But it will only work for 1 account and will probably have an issue if the adult account logged in somewhere.
Thank you for your understanding.