The series was shot and set in the early 90s, but Dorothy Jane and, particularly, Millicent had '80s Hair. Their slightly out of date looking hairstyles are a subtle way to show they're financially struggling (a hair stylist would be the least of their priorities).
As you wrote, it was the early '90's. People of all income levels were probably still sporting '80s Hair.
Fridge Logic
In the "An American Almost in Paris" episode, three American high school students (two girls and a boy) are finalists to go on a high school exchange program to Paris, France. One of the girls (Dorothy Jane) gets the best scores, but then then the selecting committee suddenly says "the family in Paris wants a boy" and thus Kirby is selected to go (making the entire episode a "Shaggy Dog" Story). But if the Oklahoma committee selecting the student would apparently adhere so literally to the gender preference of the French family, it makes no sense for the gender preference of the French family to only become clear until after three finalists are chosen—if their gender preference was such an important factor, it should have been clear before selecting three finalists...
Season 2: Molly ruins Millicent & Mary Sue room's wall driving her father's car through it, which causes Millicent & Mary Sue to move into Molly's room and Molly to move in with Dorothy Jane in the latter's room. In the first episode Molly sleeps there on a cot, as if it's temporary. The entire rest of the Season, she simply has moved into Dorothy Jane's room (bringing into it her own furniture, like her own bed), and what happened to the destroyed room is never mentioned again. The Morgans are clearly wealthy enough to reconstruct the demolished room, so why Molly and Dorothy Jane have to keep sharing a room, especially considering how much they get on each other's nerves, is unclear.
Fridge Horror
The series takes place before the internet, mobile phones and social media existed... Now combine that with the fact that the Torkelsons kids' father disappeared from their lives frequently for unspecified amounts of time, and was absent from their lives when the mother and kids moved (very abruptly, it seems) from Oklahoma to Seattle. That means that their father doesn't have their new, Seattle, address, so no idea of their whereabouts and no way to contact them... So in all likelihood, their move to Seattle means the kids never will see their father again.
Millicent probably gave their new address to some of the neighbors, or at least to Bootsie (the kids' paternal grandmother), so if Randall ever came back to town, he might be able to find out their location by asking around.
