[quote=KatherinWinter]
Problems:
1: you destroyed your own cover story within mere moments of giving it.
 How did she do that?
2: You two act nothing like siblings
Sublings act all kings of ways. some love each other some hate each other
3: I get the distinct feeling that Dante would like nothing more than to get rid of you.
how does he come to that conclusion? Dante has never said or done anything in front of anything to lead him to this conclusion to my knowledge
4: I do know that you've been influencing Aiden, and that you two are close without any cohersion on your part
How does he know that?
[/quote]

1. Bluffing - he's just telling her that to mess with her composure
2. Double bluff. He was initially fooled, but in the end, Dante himself cleared that up. Now he's acting like he knew it all along.
3. He's pretending that he's intuitively realized this. 
4. Have to thank Jasmine for this, due to her meltdown during Arts & Crafts (or was that lunch? I forget :P) the rest is a combination of common sense and more bluffing.

As you can see, over 80% of what he's telling Isabella is misinformation xD 
Also, you probably missed this, but David did in fact ally with Dante who shared information with him :D