This is my first post on any of the forums here, but I've been watching/reading for a few months and felt like throwing in my thoughts on a few of the latest issues.
On the Jonas-and-Bree-as-siblings hypothesis: I'm hesitant to accept it as inevitable at this point, because the evidence, while compelling, isn't exactly concrete. I do believe that they must have some sort of connection beyond just a chance encounter on YouTube. And I won't be shocked if something does confirm a brother/sister relationship later on. If any of the confirmed members of the Breeniverse are her siblings, I think it is quite possible Jonas is one.
I'm pretty willing to rule Daniel out as a possible brother. His parents, while apathetic, are still accounted for. After all, he is eighteen years old, was employed and a college student -- its not out of the question for them to be stepping back and taking a passive role in his life; he's an adult now. Also, even though I know this isn't definitive proof that he is nonrelated to Bree and his ethnicity/background haven't been mentioned (that I know of) in the videos, I think its worth noting that the real-life actor is half-Jordanian, I believe, whereas Jonas and Bree don't seem to have any familial connections to this region.
A few other things I'm thinking about at the moment, regarding the theory:

Jonas' parents disappeared in a weird way and there's no real proof they're gone, is there? This is probably significant, somehow. If he were just an orphan and this avenue was not to be further explored, then his parents would have died in a car wreck and been positively ID'ed in the morgue, etc., no?

Jonas appears to have money. I don't think he works, and he's got a pretty nice place with apparent rooms to spare. Where did his parents get this money...maybe some kinda payoff from the Order if his sibling (yes, I'm using the Bree-and-Jonas-are sibs-theory here) were bought away? Or maybe even if his parents sold genetic material to conceive a child they never met, playing into the IVF theory.

The gap between their disappearance and the time period in which Bree was born is another bone to pick when the sibling theory is brought up. Perhaps such a payoff had conditions of nondisclosure to it and they were violated, leading the Order to believe they needed to eliminate Jonas' parents, but they assumed that the son wouldn't know anything about it, since he was so young still at the time, and his parents somehow left information about Bree behind for him that Jonas later discovered and connected to the girl he saw on YouTube. Perhaps this is also an unconfirmed suspicious for him, as it is for us.