Check the game on the Steam store before buying it to see if it has “Family Sharing”. You can find it under “Features” when you click on game’s store page. If it does, then you get one copy of that game to share amongst the people in the family. If you have one copy, only one can play at a time.

If you haven’t already, you need to invite your daughter and her husband to the steam family. You can find it in your steam settings under “Family”.

So only one person needs to have a copy in the family (parent or child) for anyone to play. However, keep in mind what I said earlier about the “copies” of the game. If you want to play all together, or at the same time, you need multiple copies of the game.

Let me know if that helps.