Not right off hand (and if I did, I doubt that I could make a rigorous analysis of their sufficiency) but I do know that a number of knowledgable folks have expressed concern over both the governance and reserves of Fannie Mae and Freddie Mac (Including Alan Greenspan just a few months back).
Whether this is an imminent danger or just a possibility, the marginal (and many fraudulent) mortgages are immediately resold into the secondary market after they are created.
Yes they are. And they are guaranteed by Fannie and Freddie, not the US taxpayer.