The whole text
I suspect this might be easier to parse if we view this as a single piece of text, rather than four statements.
This is complicated grammar, but essentially this is a long descriptive set of dependent clauses that all modify the subjects of the sentence,
Working backwards from the subject, we see that they are 挑む-ing a 計画. Everything before the 計画 is one long clause modifying (describing) the noun 計画:
A direct translation of this whole text would be clunky as all get out.
Yet succeeded person there isn't → no one has yet succeeded
Adventure to the "forbidden land"
Taking on a plan that could be called reckless
Von Müller and Professor Barrel are ...
... But as you can see, if we translate it as chopped-up bits, it loses all flow and is quite difficult to understand in the English.
Handled as a single text then:
Von Müller and Professor Barrel are [に挑む → daring to take on] what [とも言える → could be called] a reckless plan, an adventure to a forbidden land [いまだ成功した者はいない → literally, "no one has yet been successful", or idiomatically → from which no one has returned] ...
XX とも言える YY
The crux of your question seems to be about this construction. This basically boils down to "YY, which could be called XX..."
A note about localizing
The translation you provided from the "reporter" takes some liberties with the text, but this is generally unavoidable with localization, where the goal is to produce a target text that reads like something written natively in the target language. For languages as far apart structurally and idiomatically as English and Japanese, localizing almost invariably means some deviance in word choice and construction.