Then have the most obvious companion go with Ryder, their dad. You have practically no time beforehand with your dad, all we know is that he's a strong leader and your dad. Bioware has an entire game to develop Liam and Cora, yet only a prologue to make the player feel anything about their dad's sacrifice.
As for the Kett being a thread, yes it can be established in other ways but that doesn't make them a good threat. To use Star Wars again, imagine if instead of seeing the Empire invade Leia's shuttle and seeing the aftermath of Luke's family getting murdered, we just hear about those events with Luke's only real interaction with them being a random gunfight. We see generic Kett leader do... something menacing afterwards and that's it; being an enemy in a videogame does not a good threat make. Compared to the Reapers I felt nothing except bafflement that Bioware chose to not have them have any part in the death of your dad.
I will wait for reviews, and I'll likely play the game itself come Summer, but I know poor writing when I see it and unless things change drastically I can't see myself getting over the overly generic, yet poorly written, plot.