Grant and Turner as a package would be a disaster IMO.
Yes, they'd improve the frontcourt defense but both are very poor rebounders for their positions, both want more touches on offense, and both are FAs after next season.
Of the two I'd rather have Turner, depending on the price. He provides better shotblocking and floor spacing and I think he's a better fit with Fox & Haliburton. I don't think there's reasonable a three team deal for Fox that nets Ben Simmons, but Turner would also be a better fit with Simmons, just on the outside chance that happens.
But Holmes to Charlotte for PJ Washington and change definitely makes sense.
Turner, Washington, Fox & Haliburton is a step in the right direction. The team would still need starting caliber wings but at the very least the team needs to start actually building a complimentary roster if they are really going to try and make things work with the Fox/Haliburton backcourt. A 3&D SF helps get you there.
Then they'll need to hit in the draft. Jabari Smith or Paulo Banchero are good fits at PF. Banchero would definitely benefit from a 5 that can spot up. Holmgren fascinates me though. Could he play the same type of role as Evan Mobley, as a big, skilled PF next to a traditional center? Mobley is much quicker laterally which lets him switch more easily on the perimter, but Holmgren is a better shotblocker and both are unselfish, versatile, and high IQ players.
If they Kings don't get lucky in the lottery there are several wings that should be available around their pick that could help. Kendall Brown, Adrian Griffin Jr, Benedict Mathurin, maybe even Tari Eason (who I'm high on) or Patrick Baldwin (who I'm not as high on but who should fare better in the NBA game.)
Hopefully McNair makes the right moves. Standing pat would be pretty much unacceptable at this point (I'd be completely done for this season and maybe beyond) but ill conceived "win now" moves could be worse. I don't have high hopes for trade deadline moves but I'd love to be wrong.