Ill just list what alignment I see them as and you can pick your trinity yourself.
Lawfull Good - Cassandra
Neutral Good -
Chaotic Good - Cole, Varric
Lawfull Neutral - Blackwall
True Neutral - Solas
Chaotic Neutral - Dorian, Iron Bull, Sera
Lawfull Evil -
Neutral Evil - Vivienne
Chaotic Evil -
Imho, there isnt that much alignment variations in this game, most including the Inquisitor no matter how you play him/her seem to lean towards good. Even Vivienne who I put on Neutral Evil is probably more neutral then anything, she is just quite selfish. Note though that these are my personal observations during the story, so certain characters I had less experience with then others, I talked to them as much as I could - all of them, but I think the amount of conversations you unlock depends on approval.