How to run two accounts of the same Steam game

So we are told with each copy of the upcoming game, No Man's Sky, you have your charter and start on a unique planet.

If me and my wife want to play a Steam game with an online universe off the same computer, at different times, would it be possible to:

Buy two copies off one steam account;
Buy one copy per steam account? If this is the preferred option, can they both use the same installation location?

Edit This game is not available for Steam Family Sharing

steam no-mans-sky

Best Answer

Steam Family Sharing is made for exactly this situation.

You can authorize up to 10 devices and up to 5 accounts to have (almost) full access to your Steam games without being considered the same user or using the same save files. If an authorized user (your wife, on her account) is playing on an authorized device (your computer), then she can play without you having to purchase a second copy.

Note that Steam Family Sharing cannot be used for some games which use additional CD-key or other authorization besides that included in Steam. Since No Man's Sky is not yet out, it is as-yet unknown whether it will be in this category, though personally I'd guess that it is not.