Serious questions are also welcome @upinaballoon .
I think Darius wouldn't risk killing Tommy in the van because
a) messy
b) risky
He's a man who would take no chances - what if he got stopped for a broken tail light, or hit a sheep or summat, and there TLR bleeding out in the back? Plus, you NEVER get all the traces of blood and other bodily fluids out of anywhere - and then he wouldn't be able to trust whoever he put on the "valeting" detail (because there's no way he'd clear that nastiness up himself.
And what if Tommy - a psychopath's psychopath if there ever was one - managed not to get killed first shot? Darius could end up bloodied and bruised, or even dedded himself. Doesn't want to have to explain that. And then there's the corpse to get rid of.
BeetrootMan (or Granda Beetroot as Ilike to think of him - it's cosier 😁) looks like someone who could slip a knife silently between someone's ribs and give it that special twist that severs the aorta, causing maximum deddedness with minimum fuss and minimum bleed out.
He'd probably eat him as well - don't want to waste all of that good protein (he remembers the Holodomor). He'd certainly not worry about getting rid of a body safely and discretely - I think he's done that before, and more than once.
I think possibly if Tommy hadn't been so insistent on killing Catherine, and have Ryan with him, Darius would have either sent him to Marbella, or (highly likely) at least kept him in the dark long enough for a knife to be stuck between his ribs on a boat, and the body tipped over the side.