This particular idea is an amalgamation of three different things, two of which were suggestions by Pink-Lightning. Since I don't know how to link things, I'll just have to explain them as best I can.
The first was presented by PL as an option in the interactive, "Daven's Port," under the title "Harper's Heavy Heart."
The second, PL's suggestion above, is "Big Beginnings," a world where Piper was always fat.
And the third is my own chapter in this interactive, "What if Mom was a Total Fatass?"
Now that I've credited the sources as best I can, let's begin...
The Bloating Black(s) of Beechwood Road:
In the canon timeline, the Blacks are three of the most conventionally attractive women in Daven's Port, if not all of the North Carolina- beautiful, busty, and thin. The family Matriarch, Harper, is often described as the personification of the term MILF, and has at times been been mistaken for an elder sister of Parker and Piper, rather then their mother. But, what if that wasn't the case?
In this timeline, Harper never managed to lose the baby weight she put on with Parker. Or Piper, for that matter. And Hunter? Pfft, yeah. right.
As a matter of fact, Harper has been steadily ballooning since high school, with a rather severe spike with each pregnancy. And even back in high school, Harper wouldn't have been described as "svelte" or "athletic." Harper has basically locked herself in a self-perpetuating cycle: The fatter she got, the lazier and hungrier she got. The hungrier she got, the more she ate, which in turn caused her get even fatter...
After spending all this time steadily stuffing her greedy, bottomless maw, Harper has blown up to a couch crushing, floor bending 743 pounds and can barely move. Now, admittedly, that number is a little suspect. Her girls last convinced her to step on a scale almost eighteen months ago, shortly after her accident. The scale had had a limit of seven hundred pounds even and didn't survive its brush with the elephantine matriarch, only flashing "743" for a second before breaking with a loud crack.
Regardless of the accuracy of that number, the facts remain the same. Namely, that Harper is enormous, housebound, and struggles to merely rise and waddle from room to room. Whether she wants to admit it to herself or not, Harper is totally dependent on help from her two elder daughters, and is essentially helpless.
However, while her physical abilities have been crushed under her gargantuan bulk, the family's financial situation has never been better. After Parker went to kindergarten, an almost waifish (at least by comparison) Harper went to work at Lemon Technologies, a small company which imported bulk fragrance concentrate into the city. She started as a secretary, and although she was a nearly anorexic 275 pounds, was still easily the heaviest one in the company. The constant sitting and snacking at her desk certainly didn't help matters. By the end of her time at LT, she was having Big Burger delivered to her desk five times a day...
Of course, her gastronomic excesses weren't what made her successful, though they certainly helped people to underestimate her. The company offered a Christmas bonus every year, consisting of both cash and stock. Almost none of the employees were interested in the stock, so Harper spent her Christmas money buying the stock from the other staff members. By the time anyone realized what she was doing, Harper owned 8% of company, making her a member of the board, a comfortable swing vote, and a sizable dividend cheque annually.
Taking all of this together, the Black girls were facing a very different set of challenges then their canon counterparts. Unlike reality #0 of the Hoboverse, money and calorie rich food were never in short supply while they were growing up, and given Harper's size and appetite, it's rather unlikely that she would try to enforce any sort of diet and exercise. On the other hand, Harper is also a good object lesson for the girls about the dangers of unrestrained gluttony, pinned under her own blubber, and getting winded waddling from their distressed couch to her multiple dining room chairs.
This brings us to our first choice. Do the girls learn from their mother's growing ass helplessness and mind their waistlines? Or has indulgence been firmly ingrained in the household, leaving them heavier then the canon world? And as a matter of course, a third option has been left blank for anyone who has another option they wish to consider.