Shinki addresses Gaara as his foster father in this chapter. So at least Shinki is not his biological child. More than likely the other two are also adopted by Gaara. That would explain their lack of resemblance and all being about the same age. I kind of figured Kishi wanted Gaara to remain a bachelor.
It also brings up that Kazekage bloodline crap up again since Ukyiou Kodachi introduced it in the Gaara novel and he is writing the Boruto manga. Shikadai would still be in line to replace Gaara as Kazekage since he has that bloodline and the new Sand Sibs do not.
It also brings up that Kazekage bloodline crap up again since Ukyiou Kodachi introduced it in the Gaara novel and he is writing the Boruto manga. Shikadai would still be in line to replace Gaara as Kazekage since he has that bloodline and the new Sand Sibs do not.