If you look at 1:17 in the trailer when Durotan meets with Lothar in the canyon there is no Orgrim there. So I think Orgrim has nothing with humans, he will raze Stormwind to the ground as the lore goes. It just deceives you that Orgrim might be a good guy because he is shown side by side with Durotan in the scenes.
I honestly do not know why exactly Durotan and Lothar meet because I can't find anything about this cooperation in lore. Durotan should die in this movie (1:44 in trailer, ambushed with Draka, both die) unless..there were creative freedoms. No cooperation between Orcs and Humans in the first war as far as I can read. Maybe they struck a deal to help each other in some way but then Durotan gets ambushed and killed, leaving Lothar to be pwned by the horde.
I am also confused about the timeline because Llane dies at the time of the siege of Stormwind apparently, so if that scene with the crowd is his funeral, that place can't be Stormwind because it would be already destroyed. So maybe they shifted the timeline and Llane gets killed much earlier. EDIT: or maybe it was earlier.. confusing stuff to read.
A lot of mystery still. I think movie will take some freedoms with the story and perhaps the timeline will be changed slightly. It seems they wanted to make Durotan the central character of the story, even tho it really should be Orgrim as the main protagonist. Reading the wiki on first war, Durotan seems like just a small conflict in orc internal affairs in the grand scale.