As a native speaker, I feel that in the first version:
Perché è dovuto succedere questo?
The stress is on asking why that happened in the first place. The thing was not meant to happened at all.
Perché questo è dovuto succedere?
Is more on what happened. Maybe something different could have happened instead bringing less pain.
That said, ...
The second version sounds quite unnatural. It's understandable, but verges on the ungrammatical. Even if you want to stress that it's Mario and Giovanni that are the focus of your sentence, you'd say something like:
Mario e Giovanni quali espressioni usano?
which isn't the finest of constructions, but is very acceptable colloquially to stress that you are ...
As a Central Italian, I find any construction of the form quanto + adjective + verb essere to be very strange-sounding, both in interrogative and exclamative sentences. I trust other commenters who find them utterable, and even so in limited contexts, but I'd attribute it more to regional differences than to colloquial or emphatic registers.
To source this, ...
TL;DR: The first phrasings are so unidiomatic to be ungrammatical, unless specifically meant for a reason.
More precisely, we have here a construction with a so-called “unaccusative” verb. You can see more about them in the linked article, but the gist is that in Italian there are two classes of intransitive verbs, the “unergative” ones, where the subject is ...
It's a subject-verb inversion needed to avoid any emphatic meaning. If you do not use such inversion it sounds very much emphatically:
"quali espressioni Mario e Giovanni usano?"
would mean: we know what expressions they use, but are those really e.g. vulgar, or mischievous, or damaging, ...? Come on!