[Oliver]

Originally Posted by Jan-Poo

Point1:
Why leaving Ange all alone with a sad life? Why couldn't they tell her the truth?

Possible solution:
The Ange of EP4 is not the real Ange, she's a dramatized version created by Hachijou, based on fragments of what is publicly known about her.
The true Ange never really had such a sad life, Eva told her all the truth, and she might even secretly met her family in the meantime.

I have actually first seen this branch detailed by Renall, and he was also the first one to point out Ange as the big red stop sign on the entire train of thought. That possible solution of yours works fine, but brings into doubt such a large chunk of text that precious little undoubted text remains from Ep4 at all.

Originally Posted by Jan-Poo

Point2:
Why all this time? Even if there was an "evil party X" bent on the Ushiromiya total annihilation, couldn't they come up with a plan in the meantime to solve the issue?

Possible explanations:
-For some reasons the plan actually took 12 years
-The plan was completed but they decided to never let the world know the truth. They got used to such a life? But what kind of life are they living?

That, actually, is not a very big issue. It is very likely that after Krauss' machinations, the Ushiromiya Group is worthless, and sticking with it would taint you in the business world for an eternity to come. Every adult in the family has financial troubles big enough to 'do or die', and "dying" without actually dying would be a way out for them preferable to not doing at all. Even if that proves insufficient, there is a very good possibility that bearing an Ushiromiya name itself is a ticking bomb large enough to destroy anyone's reputation forever, because of something immensely reprehensible Kinzo did to acquire his ten tons of gold -- revealing that would be a very convincing argument for vanishing and using the gold to build a new life.

Ange remains the huge stop sign though -- either we disregard her story somehow, or this doesn't work.

Originally Posted by Jan-Poo

Kinzo built a fallout shelter in the island (can you put it past kinzo? He lived during the cold war after all). In order to escape from the explosion everyone entered inside the shelter (except Eva, that might have been separated by the other for who know which reason and doesn't know about this). The shelter was meant to save everyone and so on, but the explosion was stronger than predicted and now they are all stuck inside!!!
They have been living inside the shelter for 12 years and Ange needs to go there and save them.

That, actually, is a sweet theory all by itself. Unfortunately, it does not explain why would anyone want to bomb anything.

Originally Posted by Jan-Poo

Point3
What's the point with the messages and the letters?

If the idea is to hide from the public eye and begin a new life, bottle messages would be rather detrimental to it, unless they are there to draw attention from something else...