What kind of reception would Mahariel and Lavellan receive in Tevinter?

I imagine they would be received the same way non-human Inquisitor was received at the winter palace. The Vints may appear to respect them and use proper language while in thier presence, but will secretly think of them as a lesser being.

A few may genuinely respect them for thier title as a hero, but I have no doubt several will use derogatory language as soon as they are out of earshot. And if Dorian wasn't exaggerating about Tevinter's politics, a few may send assassins purely because thier presence before them was insulting. Although I suppose if either of them was a mage, then a duel could also be an option.

I imagine Lavellan would get slightly worse treatment than Mahariel.

Lavellan killed a former Tevinter magister who was trying to transform Tevinter into a superpower the way it was in his day, and a lot of magisters secretly and not so secretly sympathized with the magister in question. At least in Mahariel's case, all of Tevinter would likely have agreed what they did needed to be done, though they'd probably still get the mistreatment mentioned above.