@Blue Lightning  
I presented no opinion here. If it’s about Inkie and Blinkie, that’s a nickname that I’ll never drop.
 
@200dogz  
I thought the ending of EqG implied that she’d never seen pony Flash before.

@Background Pony #7F37  

 
Twilight met him right before going into the portal, so he was made at the time she entered the world too; along with his backstory and memory of his past for the others around him. Afterall only real ponies that pass through the portal like Twilight would appear as an alien in that world.

As Ishizu would say, because shut up.

You are entitled to your wrong opinion :3

That, or they were asleep.
 
Or perhaps Maud moved out and Pinkie lives with Maud: not necessarily with her parents.

@Background Pony #7F37  
The movie wouldn’t have time for introducing sort of new characters for a single scene when they already had so much to do. In-universe, it’s entirely possible they’ve met off-screen.

Next you’ll be asking why Principal Abacus Cinch doesn’t have an alicorn princess counterpart.

@200dogz  
Interesting theory, but how do you explain Flash Sentry?

You see, the “Equestria Girls dimention” is actually a virtual world created and maintained by the mirror itself. Whenever someone new enters the portal, the mirror creates characters that is known to the person. Sunset Shimmer’s presence resulted in the like of Principal Celestia and Luna, and later Twilight’s visit made the human five. At the time of Rainbow Rocks neither Sunset, Twilight nor the Dazzlings had met the other Pie sisters, so they simply did not exist in the EG world.

@orochijes  
Read the description. It’s what I’m going to call them forever and ever, no matter what.
 
@DoomPony  
@Background Pony #3CA3  
True, but why wouldn’t Pinkie be showing them her friends?

Because the sequential order of canon is as follows:
 
MLP:FiM > EqG > IDW > Other comics and books
 
Limestone and Marble hadn’t been introduced as fully fleshed out characters yet by this point in EqG. So, if there were any case that these two canons conflict, MLP:FiM has the priority.
 
However, there doesn’t really seem to be much of a conflict - you could just say that they live with Pinkie’s parents elsewhere and Pinkie and Maud have their own place closer to Canterlot High.

just because they’re not seen it doesn’t mean they’re not there.
 
that or it’s not a 100% copy of pony equestria

they were sleeping perhaps?

@Background Pony #7F37  
They were in bed. Maud was only up to feed her pet.

Because those aren’t their names.

@TheAbridgenator  
It was like 1 AM on a school night and they live a strict Amish life style.

Because the producers just wanted Maud to appear to appeal to the fans. There’s no logic behind it at all.

Out, of course! Just cuz Maud is a shut-in doesn’t mean the other sisters are!