I think that reading between the lines this is a secret he told Mathilde because she's proven herself trustworthy to the point of sacrificing opportunities for advancement when it potentially contains the phrase "At Ranald's expense" somewhere along the way.
Needless to say, we should tell absolutely fucking nobody about Ranald having children, since, you know, it looks like not even most of his followers know about them. I doubt Mathilde is unique, ( Heidi comes to mind ) but this seems to be a secret that one takes to the grave, preferably a sanctified one.
I wonder how these kids are, in general. If pretty much nobody knows about them, nobody worships them by extension. Are they… mortal? And somewhere in the Empire?
Is Heidi a demigoddess? Are we a demigoddess? Probably not, but Gabriella does play the smug and slightly more successful elder sister role pretty well, despite probably being several hundred years older than us. Because of that, rather.
All aboard the shadowrunning train. Next stop is: who are Mork and Gork's parents, huh???