Tsukasa would not allow his child to be an only child, and as such, they end up with twins and a younger brother.
The twins would probably have more Western names, or names that are of famous female and male twins (Apollo+Artemis, Dipper+Mabel, for example). For this, we'll call them Kate and Nate.
The younger child would probably eventually be transfem nonbinary and, with Nene's amazing naming skills, be named Akira (暁). They'd be absolutely coddled by the twins.
Kate and Akira would both also have the same condition as Saki, which would have initially put Tsukasa into a spiral until both Nene and his sister reminded him he wasn't alone. And, unlike Saki, the two would have each other and their aunt to help when things got lonely if they needed to be hospitalized.
Overall, the whole family would be close, if not a little suffocating at times for both Nene and Akira. But the two'd have a blast beating the others in video games during family game night.
Headcanons:
Tsukasa would probably have a list of thousands of names and still not end up using any. Nene would be why.
They do karaoke once a month alone and once with family.
The bi-weekly travels to PhennyLand are mostly for Tsukasa to be a goofy dad and get promptly tackled by Aunt Emu upon entering. Nene knows this is never going to stop and so she makes sure it is even more dramatic by texting Emu when they actually arrive and are starting to get in so Emu can be there.
Late at night, Nene plays things like RPGs and otomes with Tsukasa making the decisions. One time, he picked the hardest difficulty in a game and then made the mistake of challenging her to beat it in 4 days. She did it in 2, to the panic of Tsukasa and the kids.
Nene and Tsukasa are professional actors until the kids come. After that, they work as teachers at Rui and Emu's co-owned acting school.