These are my concepts for Applejack's parents. I call them Appleseed and Citrus Heart(after all, due to AJ's aunt and uncle, one of the parents had to be an Orange, eh?).
For their bios:
Appleseed:
When Appleseed was young, his mother(Granny Smith) had already helped make their fledgeling farm flourish through the creation of Zap Apple Jam, and inspired by her, he, too, wanted to make a big impact for the family, to support it in some amazing way like his mother. But, how to do so when their farm was already famous through town as is?
The answer became obvious as he looked across the farm and the horizon beyond. He can make it amazing... by spreading it beyond their home. Beyond their town. Their family is already spread far. If he could unite them, Sweet Apple Acres could spread its business all across Equestria, supporting not only his family at home, but even his cousins, aunts, and uncles. He could unite the family, and so he made it his purpose to try.
Through his attempts to unite the business, he succeeded far and wide, finding his special talent to be farming business sense as he helped the family unite and thrive. But, his efforts took many years, and the family had many rivals to make amends with in order to strive peacefully. And it was through these efforts that he encountered the mare destined to be his wife, Citrus Heart of the orange clan.
Her kind passionate heart, natural charm, strong will and surprising strength made her hard to forget, and she helped Appleseed remember a key fact about his goals... He wanted to make the family great as a whole, but he'd been so focused upon the business that he rarely got to see his family for whom he was doing this, his ma and pa. Spending time with her reminded him of this, and got him to start sending letters back home, reconnecting with his family while the lessons about keeping those important to heart continued to be pounded into him by the mare he fell for. And not only his family, but all those that his heart cared about. Family and friends alike.
This spark of his heart that she reminded him of similarly kept her in his heart, and eventually, his great determination and grand dreams lured her to him in turn, eventually joining the apple and orange clans through their marriage.
And that's what I have for his backstory. But personality wise, it is simply put... he's the type to focus so much on the grand scope of the world that he often forgets those close to him. Thus why he fell for his opposite in his strong mare wife, the perfect balance to bring his head out of the clouds. Often ending with apologies... though the fact that he's a terrible liar makes it so he can't weasel out of any of those mistakes.
Citrus Heart:
Citrus Heart is a mare of strong mind and body. But despite this, she never aspired to much. Despite her supernatural strength, she focused more on helping others than making a name for herself. Helping her family and friends, and embracing the feelings of camaraderie among those that helped. After all, what's the point of big things if there's no substance, no heart within them?
Ironically, despite her complaints about big things being too flashy in terms of business, it's the business of her family that led her to discovering her talent. In trying to help her family, she came to learn that even businesses can suffer if its components aren't cared for. Tools and equipment often required maintenance to keep in proper working order, and she found she had a knack for keeping them working.
Just as she supports the family, she discovered that their equipment and buildings did so as well. And with her talent of understanding the little components, the finer details, along with her creative mind to help them work better, she discovered the best way to help and support her family's business, and make things easier for her loved ones. And the smiles and happiness of those she helped always meant the world to her. Even if it was just 'maintaining the status quo', as she later learned it to be called, she was still able to help maintain her family's happiness.
...which was when Appleseed came along, and threw her views for a loop. For a while, he'd been coming around, trying to change things, while she did her best to make sure to keep and maintain those that made her family happy. She and him didn't see eye-to-eye at first... but then, she learned that all of his 'business nonsense' was actually because of his love for his family, and his desire to impress them, just like his mother did him.
Through him, Citrus Heart learned that all the big flashy stuff she had scorned actually had a purpose. That not all big businesses were nothing but bluster... Some, on occasion, still sought to help others for good reason, not just for money. What mattered was balance... seeking big, without forgetting about the small.
Due to being inspired by Appleseed's dreams, she decided to follow her own... the one he inspired. That maintaining things can still lead to big things... and wanting his dream for his family to succeed, she decided 'what better way to try than to help him? It's the least I can do for downplaying his dreams for so long'. And on the way of helping him, she eventually fell for him, and him for her.
And that's what I have for her backstory.
And as for her personality, she cares for the little pony and all those that work for their family and friends. She's wise, creative, humble, and a hard worker to boot.... but as proven many times in her life, when she gets an idea in her head, she can be downright stubborn. And stubbornness with a passionate heart... can lead to big complications.
