Rarity
Rarity got married quickly to Spike and had their firstborn - Zoe Lila, half dragon, half horse. After birth of their second child, son Freedom Wings, who also is horse-dragon hybrid, the relationship became unhealthy and kids were during most of the fights between the couple. Spike and Rarity divorced, kids sided with Spike. Rarity and Spike decided to live in the same house, just they in different parts that are separated and basically two apartments. Kids are free to travel between the flats as they wish.
In different dimension, Rarity got married to Capper and together they had triplets - two sons, Dipper and Diamond, and one daughter, Gemini. Rarity in this dimension died and Gemini became so desperate to see her again, that she was the one who found portal to different universes, to find her mother again. Her wish came through only in the bitter version - she actually found her mother, but she did not recognize her and did not want to accept her as her daughter. Her brothers went after her.
Right before jumping into her best marriage, she had on and off relationship with Spearhead, when trying to seduce Fancy Pants. They had a son together, Narciss, who's very talented wizard.
Back to Rarity in main universe - after the divorce with Spike, she became colder and much more golddigger-ish. She got into passionate affair with much older Fancy Pants, who was married and had a filly with his then-wife, Fleur De Lis, but divorced her to get together with Rarity. They had one daughter, Mannuette, most likely Rarity's desperate try to secure some wealth for herself. Sweetie Belle because of these actions cut contact with her, but parents took Rarity's side, because they got part in the wealth.

Sweetie Belle
She used to admire her sister a lot, but after her actions motivated by greed, she cut contact with her and disowned her. She married her childhood sweetheart, Button Mash, and had twins with him - two little mares. Sadly, one of the twins died, so Sweetie Belle named the living daughter Faith Mash. She was heartbroken, but glad that at least one kid got the chance to live. The birth was traumatic, so after emergency C-section, she became infertile and got into bad depression. Button Mash was with her through all this and Sweetie Belle eventually recovered and changed her job to work with little fillies in kindergarten.

Next gen by yours truly.

Base by none other than X-Vintage--Owl-X herself.

Program: Paint.NET
Technology: ASUS Vivobook Flip 14, Wacom Bamboo Ink (2. gen)