Boruto has already been taught rudimentary Gentle Fist, and I'm sure Himawari is already being trained as well [probably by Hanabi], considering she awakened her Byakugan. I'm also sure that she'll hardly require any guidance, seeing how she is a natural!
Both are probably already being taught by Hinata but i would think Himawari should be entirely GF focused especially since its hinted she's a prodigy in the art even > Neji. Hima Gentle fist alongside Sage Mode bro :T_T:
Hinata's already teaching Borat and he got negged in CQC, she's clearly not doing a good job. I think Hima won't learn it, her mental impairment seems to be a major issue. And the fact she'll be killed for Borat's and Kawaki's development doesn't bode well for her
I think they both probs know the basics but in terms of mastery unless Boruto gets control of his jogan or awakens the byakugan, i gotta give it to Himawari