Hello all, new piggy owner here!

Hello,

I'm Mike and my wife and myself got 2 piggies. Never had them before.

I'm not sure where to explain my problem, so I will do it here.
I apologize if this is not the right place, so moderator please move if necessary.

So the story goes:
We did lots of reading and researching before getting the piggies.
We built them a 2x5 CxC cage, made them hiding spots, ...
Where we live it's actually quite hard to find piggies. There is only 1 place to adopt and they usually have none.
So we went to a local pet store and waited for a couple of weeks so they get piggies in.
We knew we have to get 2 males or 2 females. So we decided for 2 baby female abyssinians.
We got them yesterday evening, brought them home.
They were very scared so they refused to eat or drink, just hiding in their spots.
Next day it was a different story. They started making sounds, eating, running...so we thought it's all good.
But then one of the piggies started mounting the other one and licking and sniffing it's genitals. And it's trying to mount it all the time, and it is making noises when it's close, like maiting calls. Like every 5 minutes.
So basically the aggresive pig is eating, drinking and being "active", while the other one is shy and just running away and wants to have some space.
So I had to separate them for now until I figure out what's happening.

I'm afraid they gave us the wrong info in the pet shop and we ended up with male and female. I'm even afraid the female is pregnant, she is bigger and fatter than the male?!
Also I've read that they could fight for dominance so that's when mounting occurs. But they are supposed to be sisters from the same herd so....I don't know.....

I've taken the pictures of both guinea pig genitals. They don't look the same ;(
Can somebody who knows about this stuff look at this pics and tell me their opinion?
I would really appreciate that...