The Giana Sisters have the Merlin Sickness
They are aging backwards. The artwork for the 80s game portraits them as adult women. Now, in the 2010s, they are little girls. Extrapolating this trend, in the 2020 remake they will be toddlers.
The DS/TW Giana Sisters are the children of one of the original Gianna Sisters.
Either Gianna or Maria went on to have twin girls of her own. Finding them uncannily similar to her and her own sister, she decided to name them Giana and Maria too and pass on their love of punk culture through Giana and Maria's love of goth culture. Maybe even Giana's collection of gemstones from the DS title was passed down from her mother.
Giana and Maria's dad is at worst a Bumbling Dad rather than anything genuinely malicious
In Twisted Dreams: Owltimate Edition, a series of vignettes are added to the loading screens showing Giana being bullied and outcast at school, getting in trouble for sleeping in class and bringing a doll with her, her father arguing with the teacher after she presumably gets suspended and then him ranting and trying to bust open her door at home with Maria protecting her. While most people took this to mean that Giana's father was emotionally abusive, the fact that Giana's father was shown chewing out the teacher when he got her implies that he does care about her wellbeing. How he appears in the following scene most likely is a distorted interpretation of him based off how she and Maria felt being punished so harshly.
