One day, I shall complete my next gen guide. but for now, tidbits.
Rarity's family is a bit complicated to say the least. For a while, she was single, focusing instead on expanding her business. She had some flings and dates here and there but never had children. Then she met to street urchin named Crescent Moonstone. The little filly tried to rob her while Rarity was visiting a friend of hers but soon collapsed from hunger. Rarity took her home and fed her. After a few days of nursing the filly to health, Rarity chose to adopt her.
Crescents parents are important but I don't feel like revealing them yet. It's a secret. Her mom is a unicorn, obviously. Her dad, however, is a Pegasus, which is why she can puff up like other pegasi despite being a unicorn. Also, crescent always wears something around her neck because of a mark on her neck. Rarity assumes it was made by the filly's mother in an attempt to kill her.
Hon is a mystery. Rarity only says that she had mated with a dragon but for some reason, he couldn't come with her. She refuses to tell anyone his name, where they'd met or why she chose to have a child with him. She does claim to love him dearly though she later marries someone else. The birth of Hon caused some strife between Rarity and her parents though Sweetie adores both her nephew and niece.
Hon thinks Crescent is his big sister. Crescent adores her baby brother and will kill anyone who messes with him. Only she's allowed to torment to little twerp.