player.setHeadBlend(Number shapeFirstID, Number shapeSecondID, Number shapeThirdID, Number skinFirstID, Number skinSecondID, Number skinThirdID, Number shapeMix, Number skinMix, Number thirdMix)
Shape / Skin First ID: "Mother"
Shape / Skin Second ID: "Father"
Shape / Skin Mix: Float values ranging from 0.0 ("Mother") to 1.0 ("Father").
Third ID: If you feel like another ID should be mixed in. Personally I leave 3rd IDs to 0 and 0.0f mix. Basically they appear to relate to the parent / legacy character customization in GTAO.