Olivia gets two, Mia gets only one

You bring them to the laboratory where you first transformed Doe. You tell Olivia, the most eager of the two, to take off her clothes and lie on the table. Olivia strips out of her clothes and you quickly see why she was send to a brothel. Despite having a slim figure, she has curves in all the right places. While Doe has only a C-cup Olivia easily has a DD as well as a nice round butt.
Once Olivia is nude, she eagerly gets onto the transformation table. The same table Doe got transformed on.
You grab some hairs of a red fox, just like you’ve done for your first test subject, and bring them to Olivia.
“So … that’s going to turn me into a foxgirl?” Olivia asks excitedly.
“These hairs hold the genetic code of a red fox.” You explain. “I will merge it with yours and then they will spread, replacing all the human DNA in your body with human/fox DNA hybrid.”
“Wait.” Olivia says. “Does that mean, my hair will turn red too?”
“Doe’s hair turned brown.” You say as you look at your first foxgirl. “So I guess your hair color could change too.”
Olivia takes hold of some of her hair and looks sad.
“You prefer keeping your hair color the way it is?” You ask.
Olivia nods.
You reach for Olivia’s head and grab one of her hairs at the base. You gently exert **** until you pull it out. You roll up the long hair and add it to the fox hairs.
“I’ve never done this before. So I don’t know what will happen.” You say. “Let’s hope it’ll work out the way I plan it.”
Olivia smiles and nods.

You place the hairs onto the woman’s stomach. Olivia, curious about what’s going to happen to her, looks at her belly. Doe is looking too, eager to learn about the spell that changed her life. Mia is merely looking from a distance. You then place your hand over the hairs and summon your magic.
“The spell starts with a summoning of both life magic and water magic.” You explain to your foxgirl apprentice.
Olivia starts to glow and breath heavily.
“It’s happening. I can feel it.” She says.
“The former is because I’m going to change her biology, the latter is because it’s easier for the foreign DNA to be absorbed when it’s in a liquid state.”
Olivia’s belly then becomes like liquid. Both her and Doe see the hairs sink into her skin and disappear.
“Now I need to use black magic to break the DNA strains apart.” You continue explaining. “DNA is like two hairs twisting around each other. One human helix and one fox helix. With the help of black magic I can pull them apart. Two human strands and two fox strands. Then I switch them around, paste the human strands with those of a fox. This time however, I’ll first combine the fox strand with some DNA of the black hair I added. Then I’ll merge the human and fox strands to form a human/fox helix. Next, I use light magic to burn away the impurities and life magic to heal them again.”
Doe looks attentively and at her friend’s belly and nods.
“Finally, the most difficult part. I cast a spell to temporarily have the merged DNA cell relentlessly make copies of itself. It’ll put those into the equivalent of virusses which are then released into her bloodstream. They will then find cells with pure human DNA and inject the new helix into them, destroy the old human helix inside it, replace it with the new one and start producing viruses as well.”
“So basically … you turn a cell into the equivalent of a sperm producer and the viruses it produces are like sperm which then go and impregnate all of her human cells?” Doe says.
“… I guess you could say that.” You hesitantly admit.
“Oh my god!” Mia says, having hear your explanation. “My entire body is going to get impregnated?!”
“That’s … actually kinda hot.” Olivia says.

As the lot of you watch Olivia’s ears start moving up her head. They become large and pointy and black hair starts to grow all over them. From the base of Olivia’s tailbone, just above her butt, two fleshy lumps start to grow. They elongate and grow into fleshy tails. Then a whole lot of long black hairs growing from them, giving her bushy foxtails like Doe. At the same time some of her teeth become just a little sharper, especially her canines.
When the transformation is done, you stop fueling magic into Olivia and pull your hand back.
The former prostitute quickly sits up and puts her hands on her new ears. Then she sits on her knees and looks behind her to see her tails. She grabs one and holds it in her hands.
“Oh wow. I’m a foxgirl.” She says. “And my hair is still black.”
Olivia then jumps off the table and hugs you.
“Thank you so much.”
You hug the naked foxgirl in return and hope Doe doesn’t notice your erection when Olivia pulls away.

You then tell Mia to undress and turn to your workbench to grab some more fox hairs. Only this time your eye falls onto a box next to it. There’s a label on it saying ‘Fennec’. A fennec is a type of fox that is a bit smaller than usual foxes. So far every time you turned someone into a fox-person you used the DNA of a red fox. Maybe now would be a good idea diversify and have Mia be a cross between a human and a fennec.

When you turn to the girls Mia is already naked. The chubby girl is holding her hands in front of her chest and groin to hide her girl-parts. Though it’s not like she’s got much to hide.
She lies on the table like Olivia did and you infuse the fennec hairs into her belly. Like expected Mia’s transform is a bit different. Her ears are longer and pointier, she has only one tail and it is a bit thinner.
After the transformation, when she’s checking out her new body, you manage to check out her boobs (or what little she has). The poor girl clearly hasn’t been blessed by nature.