Nope, those are not twins. That is the same pony, Fallen Ashes (or Ash). In my canon, bat ponies have a bit of magic, they are able to cast illusions/hypnosis (like vampires) as well as do some night weather-related things like Pegasai. In Ash's case, they use an illusion to make others see them as a stallion sometimes. This is due to Ash being genderfluid. They don't mind any pronouns really (commonly referred to as 'her' but accepts to 'him' and 'they'), but some days feel more like a stallion or more like a mare (or neither), so they like to cast an illusion to look like a stallion to others when they feel like being a stallion at that time.
Ash is an orphan, and one of the few bat ponies living in Ponyville. They were found on Rarity's doorstep in a basket with a note when they were a baby. Rarity took them in, filling a void in her that she thought her prince charming would fill. Since then she has stopped dating and has been raising Ashes, with help from the rest of the Mane 6. When Ash discovered their powers of illusion (and gained their cutiemark), Twilight brought a member of Luna's Royal Guard to mentor the young bat pony in controlling their power.
Now, Ash is a teenager. They love their mom Rarity, who adores them back, and have learned valuable lessons on generosity from her. They're also a bit of a flirt, but hardworking (despite their slender appearance). They are nocturnal instinctively but have been raised on a normal pony schedule. This leads to sometimes staying up late at night and then nodding off during the day, even in school.
(Note: I'll try to refer to Ash as 'them' mostly but I may refer to them as 'her' in other cases and when depicted as a stallion refer to them as 'him')