Takeko and Yuko's names were taken from the historical Nakano sisters of the same names, as seen
here. - Mahouishii Takeko is 30, a badass warrior & general and widely considered her father's heir. She was the one who initially captured Sephiroth when he was 15. She's admitted to him, though not where anyone could hear, that she doubts she could have done so if Sephiroth had been a little bit older and more experienced. (She's not quite right about that. In On Broken Wings'verse, where things proceeded according to canon, she
did capture him a bit later, when he was 16, but he escaped after a few months.)
- Yuko, 24, is the 'lady' of the two of them, although she's no slouch with a blade either. She's open about the fact that she values her freedom too much to ever want to be daimyo, and she's grateful for her steady older sister to take that role instead. However, Takeko can be a bit blunt for the delicate sensibilities of her fellow nobles, and that's where Yuko's talent at diplomacy comes into play. Yuko considers it a game of sorts, to ferret out people's secret desires and use that knowledge along with Just The Right Words to get people to do what she wants and have them think it was their idea. (Takeko and Seph are baffled by this ability.)
Both of them have children: Takeko has a daughter, 8-year-old Suzume ("sparrow"), and Yuko has twin sons, Nezumimaru and Torimaru ("little round mouse" and "little round bird"), 5. (Torimaru is considered the eldest, i.e. he came out second.) They're just normal little kids, as normal as you can get when you're the grandchildren of a powerful daimyo at any rate. And they love having an Uncle Seph because Uncle Seph will go along with pretty much anything. ^_^
Despite the presence of children, neither Takeko nor Yuko are romantically linked with anyone, because it's my story and I've decided they can do that.