Simple sketch ~
It's not really serious headcanon I guess. Just my supposed vision of Pinkie and Pie family's biography.
I'm not interested in hard developing headcanon but why not draw sketch of this, right?

p.s. all MLP fanart artworks appear a little earlier on my Boosty [for "Coin" subscription's level]
I don't draw like this very often but sometimes it happens. And various WiPs, sketches can be seen there before than other places. And also full size of fanart pictures will be stored there. WiPs you can see with "Penny" subs lvl

• Parents •
○ Cloudy Quartz
- middle-aged [maybe ~48-50 years]
- pureblood earthpony
- pinto, partially white [not gray] hair
- standart mare

○ Igneous Rock
- middle-aged, older than Cloudy [maybe ~52-55 years]
- pureblood earthpony
- dapple, gray hair
- standart stallion

• Daughters •
○ Marble Pie
- young [~18 years]
- pureblood earthpony
- pinto, has partially white hair
- shorter than average, slim + weak

○ Limestone Pie
- young adult [~24-26 years]
- pureblood earthpony
- partially dapple with three white socks
- average mare, standart bodytype but strong

○ Maud Pie
- adult [~28-30 years]
- pureblood earthpony
- basic coat with one white sock
- taller than average, slender but stronger than average

○ Pinkie Pie
- young adult [~ 20-21 years]
- earthpony, not own daughter for Pie couple
- shorter than average, chubby

Yeah, I think about Pinkie can be adopted kid. Pie's family is her family too but they are distant relatives. Probably her parents were gone or something else and little Pinkie was forced to stay with the Pie family. They raised her, but they didn't become real friends for her. And also she is very different in appearance and character from them cause her real parents were very positive and bright like her, not like family from Rock Farm.