Joke explanation bellow:
In Legends before he became a cyborg Grievous was warlord of a planet that practiced polygamy. You do the math.

(Maybe something like it is true in canon and we'll have descendants of Grievous in Rebels or other stories)

I do think getting a Kaleesh character (doesn't have to be related to Grievous) in the empire era would be a great addition to the new canon. They watched as their friends and family starved due to the Republic, had their hero turned into a cyborg then sent to his death by the Separatists, then the Empire comes in and most likely oppresses their people even further. Would they fight for the Rebellion to make their own future or see it as just another government waiting to screw them over?