Well the new updated faction packs has me thinking and leaning into a certain idea for my Red Hunters.  My Howling Griffons are Ultramarine Successors and My Exorcists are Imperial Fist Successors, the Red Hunters have no Parent Chapter listed so I can use any Chapter I want or No Chapter at all.  I am leaning towards Dark Angels. I like the following Detachments as I feel it fits their Belief that the Emperor is a God. 

Interrogation Conclave

1 Detachment Point

▪ In the Fight phase, when a friendly CHAPLAIN unit destroys an
enemy unit, enemy units within 6" of that CHAPLAIN unit make a
battle-shock roll.

▪ Friendly CHAPLAIN units have the following ability:
Sower of Dread (Aura): While an enemy unit is within 6" of this
unit, that enemy unit has -1 Ld.

Restrictions: Your army can include DARK ANGELS units, but it
cannot include any ADEPTUS ASTARTES units drawn from any
other Chapter.

Enhancements

LIMITLESS ZEAL
This Interrogator‐Chaplain is restless and dynamic, not
only in his pursuit of enemies but also when eliciting their
screamed confessions.

CHAPLAIN model only. This unit has +1 to charge rolls.

INESCAPABLE INTERROGATION
Whatever physical obfuscation the enemy hides behind mirrors
only the lies shrouding their souls. This experienced Chaplain is
deceived by neither.

CHAPLAIN model only. This unit’s ranged attacks have
[IGNORES COVER].

My other points would be the Librarius Conclave (another 1 point Detachment) and either Fulguris Task Force or Darkflight Pursuit since both are Land Speeder based detachments.