I know some personalities like heroic can be obtained by simply visiting CoS or RoM. The wormwizard one from FL HM is difficult to get solo, but there are people who completed it.
Atleast the final boss
If you can solo vFL HM, I think Hodor will provide you some excellent tank, healer and 2nd dps to get that personality
Well, there is video over there how DK managed to solo final boss with wings, but there are too many "interrupt mechanics" on the way to do it in one person.
"Sheggorath, you are the Skooma Cat, for what is crazier than a cat on skooma?" - Fadomai
I want to know how the *** are people capable of soloing these things in the first place.
Like... Are you robots? Because you definitely don't seem human
And if you are human, then... Divines help you.