I think Microsoft clarified a lot of
this here. On the giving games away it is very clear:
Notice they specify disc-based games rather than all games and levy two requirements - games can only be given away once and it is only to people who have been your "friend" for a while. Basically, this is to prevent private sales (i.e. you sell it to me and then "give" me your copy online).
Also, it is publisher dependant - although Microsoft specifies for games they publish:
So basically, a game may only be "given away" once, to a restricted number of people, and it must be approved by the publisher.
Sharing is where it gets more difficult. They state that anyone can play the game on your console. Pretty much the same as PS+ or XBox live digital games right now (e.g. my wife can play all of my digital games under her PS account as long as she is using my machine). Then they have their special "family access". We don't have details to that other than it will allow your entire family to have access to your library.