Let’s say you have twin children, and your whole immediate biological family uses Unity, each with their own computer. Must everyone get a license? Is there any sort of family discount?
that rocks on so many levels. they ought to give you a discount just for saying that. change it to my (cough Jeff) and it’s a tshirt sale. 
As it stands, yes - each person should get a license. The license is one seat - two computers.
There’s always the odd chance that you can work something out with sales@unity3d.com, but I highly doubt that you’ll get a discount (unless I underestimate the size of your family 
).
Hi Jessy,
If this is some sort of roundabout announcement about you and your fiancee, congratulations!
Ha! Not quite!
I’m just looking for a clarification of intent (for now :)).
Unity is licensed on a per-developer basis so each person using Unity to create content needs to own their own license. We don't have a formal discount program for commercial sales in volume, although we are open to special discounts for those buying in volume if you're buying ten or more licenses at once. Contact sales@unity3d.com for additional information.
With the above in mind, like any rule or law, it all boils down to an effort of enforcement. Despite the laws to the contrary, I can speed on the roadways all I want, until I get caught and the one who catches me chooses to enforce that law (do I actually get a ticket? a warning? or a thumbs up 'cause the officer likes my motorcycle?). In the case you describe I doubt we’d take enforcement action so long as it’s limited to your family experimenting and generally “playing around” with Unity. If anyone ever begins to move towards actual content production for release somewhere then we trust that you’ll do the right thing and buy a license for that person (or people).