Yes, there can be two nouns in the same position in a sentence. The two nouns here are part of a noun phrase in the subject position.

The “of” construct here is just another way of showing possession. You can also say, “The task’s severity...”

Personally I would treat 1=''The severity of the task ahead'' as a noun.

One could then say that 1=''the difficulty'' became apparent.

I don't know what the grammatical name for it is. I would call it a 'noun construct'.