Drawing more ponies to deal with stress! Up next we have the royal heirs of the kingdom: Sundance, only daughter of Princess Celestia and Discord, and Eventide and Moonlight Sonata, the children of Princess Luna and Rockhoof. All three of them are very close, though Sunny and Moonlight are notoriously public shy.
Some more info on them!

Name: Princess Sundance
Nickname: Sunny, Sunflower (only called this by Celestia)
Age: Adult
Pronouns: She/her
Parents: Celestia and Discord
Cutie Mark: Doesn't receive one, but if she did get one it would probably be a mark for empathy or compassion
Bio: Despite being the only child of two of the most powerful (and prank loving) beings in the kingdom, Sunny is very shy and gentle. Growing up, her parents were very protective and unintentionally isolated her from making many friends. This is due to the fact that Sunny was kidnapped when she was very young by an extremist group who disapproved of Celestia's partnership with Discord. She was found fairly quickly, but it had a deep effect on her parents and how they raised her. Sunny is very nervous around ponies she doesn't know, despite a desperate desire to make new friends. As a result of her isolation, she is very very close to her quiet cousins Eventide and Moonlight. She is very intelligent and well read, and has a deep guilty pleasure fondness for romantic novels and movies. She loves her parents a lot, but is frustrated with their coddling; Discord swings wildly back and forth between joking around so much that he knocks her off balance and being incredibly over protective of her. Celestia's moods are more balanced, but she can coddle her daughter to the point of being cloying. They've both gotten better about it over the years, but it's had an undeniable effect on Sunny.

Name: Princess Eventide
Nickname: Evie (only her closest friends and family get to call her this)
Age: Adult
Pronouns: She/her
Parents: Luna and Rockhoof
Cutie Mark: Constellations, in particular designing new looks for the night sky
Bio: The oldest of the heirs and the one who spends the most time in public. Eventide is quiet and thoughtful, very sure of herself and her decisions. She's a steady rock for her more emotionally fragile cousin and brother, but doesn't baby them (Sunny in particular) as much as their parents do. Evie can be stoic to the point of stiffness and can come off as rude to ponies who don't know her well, but she's very caring and goes out of her way to help anyone who asks. She may look short next to her extraordinarily tall relatives, but she also towers over most ponies; she just happens to be the shortest of this bunch. She is very close to both her parents, but spends a lot of time designing new constellations with Luna and studying the science of the night sky.

Name: Prince Moonlight Sonata
Nickname: Moonlight
Age: Adult
Pronouns: He/him
Parents: Luna and Rockhoof
Cutie Mark: Gardening, with an emphasis on night plants (he does have a cutie mark, I just haven't designed it yet!)
Bio: The youngest of the trio, though pretty close in age to Sunny. He's also very shy and introverted, with an extreme dislike of large crowds and the meanspirited gossip of Canterlot. He rarely makes a court appearance, preferring instead to spend time in his night garden tending his plants and flowers. He has a surprisingly delicate constitution in the sun, and will often pass out if he has to spend too much time outside on a warm day. He and Sunny are very close, and often commiserate over their shared dislike of interacting with new ponies, though he doesn't have as strong a desire to make friends like she does; he's happy with his family and his garden. Of course this all changed when a fiery pegasus crash landed right into his hydrangeas and his life one night. Dragonfly, Fluttershy and Rainbow Dash's oldest daughter, accidentally landed face first into being one of the only outside ponies to befriend the Royal Heirs. She and Moonlight are close in particular, though it takes him some time to admit that he enjoys her company over the previous peaceful silence of night. One day he'll figure out why his heart beats so fast whenever he sees her land in his garden at night with a cocky grin or why she blushes when he clucks over her injuries from her run ins with various dangerous creatures, but it'll take him quite a while to come to terms with it.

Fun facts:

Sunny's tail isn't actually like a horse tail, it's more like a cat or fox tail! It can wag and emote much more then your average loose haired horse tail.

Moonlight's mane isn't white, it's a very pale silver and is emitting a constant gentle glow, which is more noticeable at night. He usually keeps his tail pinned up since it gets in the way while he's working and if he does have to go someplace that has other ponies, they often touch it without asking him which he haaaaates. He does like the silver and glow, which is the only reason he hasn't cut his mane or tail extremely short. His hooves have a glitter of stardust.