|Screenshot of Mr. and Mrs. Cake with Pinkie Pie from Season 1, Episode 4, "Applebuck Season"|
Lauren Faust gave a little insight into the relationship between Pinkie Pie and Mr. and Mrs. Cake on her deviantArt page. Here are comments from April 19-20, 2011:
I'm curious- In what way is Pinkie Pie related to Mr. and Mrs. Cake?
*fyre-flye [Lauren Faust]
They are not related. Pinkie was always their best customer, and always hanging around anyway so they let her rent the loft upstairs. I think they probably pay her partially in sweets. They love her like a daughter, though."