so if i got it right
frieren - wing gundam - the head, armor skirt and legs are clearly those of wing gundam
himmel - gundam mk ii - the head and legs are clearly of the gundam mk ii
eisen - rx-78-2 gundam sd - obviously it is an SD gundam but the eye shape and faceplate makes me think of grandpa gundam
heiter - gundam deathscythe (i'm not sure here) - i have the bias of the black color and how the cloak reminds me of deathscythe hell plus thematically it fits with duo's priest clothes, but i'm not sure since i don't feel the head is a 100% match to deathscythe, deathscythe hell, deathscythe hell custom or the endless waltz version of deathscythe