1. Nobody yet knows the answer. It was discussed a lot in Div2;ED section and on our russian forums (ag.ru) bur so far no solid theory has place. Mostly, ppl agree that either Ygerna possessed Talana or there was NO real dragon powers offered to the hero. It's indeed looks like a hole in the plot.
2. First, I'd like to clarify some things: DK != dragons. The real, true Dragons is a different beings. I remember it was mentioned in some book that they almost gone from the Rivendell. Cosider the fact that almost all their descendants (Dragon Knight) were killed by Dragon Slayers it's understandable why everyone calls you as the last DK. Since you're the last one.
Btw, the The Ouroboros was the last real Dragon Knight (he obtained the power from the dragons himself). Note how BIG he was. Almost like a Dragon.
