In the new story concept I'm working on, I wanted to come up with something really unique for a fusion. I would love feedback on the characters, scenario, and transformations for this section of the story. The following is an excerpt of my notes thus far.

Subjects: #4 - A 23 year old girl (girlfriend of #5)
#5 - A 25 year old guy (boyfriend of #4)
#6 - An 18 year old girl (#4's sister)

#4 and #5 - A Mastodon Squid-Naga. 2 stage transformation.

First, #5 is turned into a genitalized mastodon. Gains massive bulk, large legs, feet, big cock with sheath, large swinging testicles, trunk(with nose), and penis-tusks. #5's intelligence is slightly diminished.
Then, #4 is turned into a cuttlefish-like creature. Her arms split to become 4 short tentacles (what kind of tips? Suckers, prods, animal cock, etc…?) Her mouth becomes a toothy maw. (This is to make her like her somewhat fearsome new form, a setup before the fall.) Her body liquifies and compresses down to a conical tube. Her asshole moves to the tip of her head and her vagina moves through her body to rest on her "forehead". Her boobs shrink and stay underneath her.
Post transformation,  Slavers allow #5 to fuck #4 senseless, like an animal. While they are exhausted from orgasms, #4 feels a large, lubricated butt plug entering her anus. Then she is lifted up from the ground and the other end of the apparently double-ended butt plug is inserted into #5's rectum. Her handlers let her go and she hangs from his ass, held by the plug. She/they struggle. Then a new transformation begins. #5 loses his rear legs, adding to #4's bulk as she elongates, becoming a more proper tail. But the double-ended plug dissolves and merges them together permanently, a direct conduit from his colon to hers. His digestive system wins the pitiful battle for control of the new shared body. #4's innards simplify. Her teeth recede and they shit out the excess mass. # 4 bemoans her fate as an anus. Her breasts migrate to become a second set of testicles. #5's mouth becomes a pussy, and his trunk gains a very stretchy mouth, allowing for vore-type action and breathing. #5's front legs bulk up, they will be the primary means of transportation. # 5 gains breasts as well.

#6 becomes a shrunken fuck nugget. No eyes (maybe frog like eyes or eyes on a stalk?), nose remains. (Gotta leave them a way to breathe and gag on cock.) A large sucker mouth, boobs replace her arms and legs. Vaginal play is super tight, feels good, bit doesn't compare to anal. Anus to mouth are 1 truncated tube. Through and through is common and feels best to the user. Is a disappointment to her new owner. Is given to a pet, her newest pet, the combined #4 and #5 (#5 has no qualms about fucking his anus' sister.)

So, what do we think of the final creature?
What do we think of the change to their relationship?
Please, any feedback helps me make better content for you, my readers.