You signalled the Knight Bus and boarded, telling Stan Shunpike 'Patil Residence' as you paid the fare. It didn't take long to get there. You disembarked and walked up to the house. You walked in the front door and climbed the stairs quietly. You came to one of the doors, but didn't enter or knock. Instead you listened to the voices inside.
"Sometimes being twins sucks." said Parvati
"Yeah. I don't know why our magic won't let us have separate animagus forms." agreed Padma
"Okay, so that's the potion for the dominant role, and that's the potion for the submissive role." said Parvati
"Yeah but how will we decide who gets which one?" asked Padma
"I have an idea. How about if a guy our age that isn't family walks through that door in the next two minutes, he can become our Master, and he can choose for us." suggested Parvati
"Okay, but we should make it a binding magical oath, so there's no backing out." said Padma
Parvati nodded.
"I, Parvati/Padma Patil, swear on my life and magic to obediently serve any man to cross this threshold in the next 2 minutes as Master forever, so long as his age is near ours and he bears no significant blood relation. So mote it be!" they chanted out
You waited until they finished, and opened the door.
"H- Harry, what are you doing here?" asked Parvati
"Well I believe I needed to cross the threshold into your room to obtain Mastery over you lovely ladies." you said
"If you want us to serve you, you have to decide who gets which potion first." said Padma
"Alright, then. Parvati, you take the dominant potion, and Padma, take the submissive potion." you decided
The two girls nodded and collected their potions and drank them quickly. Their bodies became stiff. Parvati turned away from Padma, and Padma bent over at a 90 degree angle. She lurched towards Parvati, and they seemed to fuse together at the collision point. Still in that shape, their bodies melded into one: a beautiful brown furred mare with a black mane. It seemed like in response to their new ownership, their clothes had transfigured themselves into a saddle, bridle and reins.
"In this state, I think I'll call you Nimbus, after my broom that got wrecked. After all, It isn't fair to use just one of your names, and a mix of the two would sound weird. Also, I think you're my new favourite means of transportation." you said
You led them out of the house, and hopped into the saddle. Where do you want to go?