Hello.
Well, this group is exclusively related to the original Mane 6 characters, in other words, the ancestors of the Mane 6 characters from the new MLP FIM. They are the original characters and the inspirations, thanks at them they where created. They are the ones who should have been the Mane 6 from the new MLP. But for copyright issues this wasn't possible, and now they remain as the "old" and "original" ones.
That's why this group only includes and is related to those 6 ponies.
I hope you understand and I explained it well.
But this yes, I own other MLP G1 groups as well and I'm the founder. There's one which is about the whole MLP G1 franchise and there yes includes Megan and Tirek.
I don't know if you seen it, but in case you didn't and you are interested, here is:
g1-my-little-pony.deviantart.c…