It confirmed that they are both the youngest. Marble younger than Pinkie by a few minutes. But they're definitely not identical twins. So simple question, How?

4964736 You are aware that twins just means 'born at the same time', right? Twins are not necessarily identical by any stretch of the imagination.

That is because they may be Fraternal or non identical twins which are in fact a thing. This article explains the basic differences between identical and fraternal twins but the main difference is that identical twins have the exact same DNA while fraternal twins do not even though they are of course closely related.

https://www.healthychildren.org/English/family-life/family-dynamics/Pages/The-Difference-Between-Identical-and-Fraternal-Twins.aspx

4964743 Yes but they are so radically different that it's almost insane to think that they're that close that pinkie talks for marble on occasion.

4964749 The same could be said of literally everyone in Pinkie's family. She bore witness to an unnatural manipulation of the very spectrum of reality at an insanely young age, embodies laughter so completely that she can wield it as an elemental force, and her destiny is intertwined with the very fate of Equestria as a nation.

Of course she's not going to be a thing like her twin sister.

4964758 If you remember pinkie has a darker tone to her when she doesn't have her bouncy personality and I mean her actual coat and mane color grows darker.

4965458 Actually they turn dull when she is like that. Still it kind of is like she can be two different ponies.

4965458 What does color have to do with anything I said?