Can't say i know the series THAT good, but didn't he expect the heritage to effectively "not matter much"?(at least for much longer)
In regards to Tenchi... depending on the continuity no, the grandfather was hiding out on earth, and simply did not feel about informing even his kin of what he and they were. So in one continuity, lack of knowledge and training caused tenchi to loose his mother Atchika
In another, he did not know anything was up until Kagato attacked and stole Ryoko. Even then the Grandfather did not help but told him it was omething he must do.
Yeah, REAL smooth...
Well... that was Genma and Soun for you. Sadly Soun tends to get overlooked, despite knowing of Ryogas curse and setting up multiple engagements for his daughters like Genma...
Because he's such a genius that he HAS to plot behind everyones back to make things happen like he want them, or he wouldn't feel like such a badass evil overlord!
The in canon explanation was Gendo and Fuyutski wanted Shinji to fail, so the Evangelion would go berserk... They bet the fate of humanity on the idea Yui cared enough to intervene directly, rather than train him to fend off the angel.
IIRC, she did seem to expect him to simply do the job.
Granny Hina is a sore point with me, as I view her as the most evil and backstabbing character in the Love Hina story due to her manipulations and entrapment... but fanon rarely calls her out on it, as she is generally safely gone when the fireworks begin...
I can PM my notes on it, but i'll not post all that here as it would be too off topic.
In many instances, these powers and/or transformations are supposed to remain secret to others at large, and not preparing them could potentially be asking for things to blow up in their face. Like, say, someone reaches the age of sweet sixteen (I don't know why that's a trend...) and gets access to magic, but without proper training and understanding they use magic unintentionally and cause all sorts of grief. Or, say they become some mythical creature and freak out, and end up exposing themselves to the public.
It should be noted Tenchi lost his mom in the first Tenchi movie due to that. Katuhiko decided never to inform his daughter of her abilities, her family history, or train in anything other than Kendo... she was unprepared for Kains attack and very nearly died... Washu erased the memories, but the huge untrained outpouring of her Jurai energy shortened her life so she lived long enough to only see Tenchi born and get to a few years old.