Fundamentally, you and I are thinking in different timeframes. I understand your position concerning now, and possibly next April. Longer-term, though, based on everything they've shown to date - in the minors and the majors - I think it's pretty likely that Bohm and Kingery become our full-time 3B and 2B.
Hernandez will be gone in a year (after 2020), and given the downward trend in his OBP, I think it would be unwise to extend him. It looks like he peaked at ages 26-27 - which wouldn't exactly be unusual.
Franco may peak (this year? Next year?) at a somewhat higher OPS than his career .735 - maybe he'll have an .800 OPS year (particularly with the current baseball!), but after that peak, I anticipate a fairly rapid decline.
So the question, to me, is not whether Kingery and Bohm will replace the incumbents; the question is when. I'd certainly want Bohm to force the issue - I wouldn't move Franco this month to "make room" (well, unless Klentak gets an offer he can't refuse!). But when he does force the issue, there should be no hesitation.
Similarly with Kingery - until/unless he shows that what we've seen this season is a mirage (as opposed to what they expected when they signed him long-term), he has to be in the lineup. If they find a reasonable alternative in center field (Haseley? Not right now, evidently; a trade this month?), then I would want to see Kingery at 3B (notwithstanding his arm), or at 2B if Franco is in a hot streak (when he's off, he's pretty awful). But longer term, if Bohm displaces Franco (which I expect), 3B will not be an option for Kingery, and he will displace Hernandez (better now; younger, still improving). Barring injuries; barring trading somebody away, of course.