Trilogy on Origins? That's too short to make it work as is. The scenario needs radical adjustment, and meaningful cuts way over my paycheck.
Right now the formula I'm considering is to have Ostagar happen at the middle of the second movie, and have the story being told with Alistair as the constant, as a Watson to Duncan's then HoF's Holmes.
Ep 1 would be Redcliffe, Darkspawn Invasion, Haven (meeting Leliana) and Sacred Ashes. Party would be Duncan, Alistair, Leliana (merged with Genitivi) and Jowan (traitor).
Ep 2 would be mostly Dwarven Origin (merged with Oghren's) -> Ostagar -> Orzammar & Deep Roads. Party would be Alistair, Warden, Dog, Morrigan and Branka.
Ep 3 would be Flemeth's Grimoire, Lothering (meet Leliana again), Landsmeet, Ritual and Archdemon. Party would be Alistair, Warden, Morrigan, Dog and Leliana.
Ritual would be offscreen between Alistair and Morrigan. Leliana would be singing to Warden after the Landsmeet. The only romance we get to see is a growing one between Leliana and Warden, as the two women grow closer. The ritual is implied. Alistair might be falling for Morrigan as well, but we don't know for sure.
Loghain claims the right to a duel. Dog fights valiantly and wins.
I'm not sure about the Warden's personality. It would be a female dwarf. She would be disillusioned, betrayed by her brother (Bhelen), by her ex (Branka), and pretty much ready to do anything to save the world. She would cut the crap in discussions and impose her views, firmly and voluntarily, much like the Inquisitor does. She would always take the path of least resistance, letting her strong ethics (and utter lack of honor) take hard decisions in her place.
The choice of a dwarven warden is entirely based on the decision to feature the Deep Roads rather than the Circle of Magi or the Brecilian Forest, and this is in turn entirely based on the choice to feature a darkspawn fights on every episode, and to have a downer episode in episode 2.
I have no idea how to feature the human noble or the city elf origin, and I don't think the dalish elf origin would work with only 3 movies. I think Magi and Dwarf are the only origins that can be fit in a trilogy, and they're pretty much exclusive.