THere's very little I'd think of changing here. It's possible to imagine a more regular meter, which I might find more pleasing to the ear, but that's not where Rilke went. I don't like tombs much at all, but graves is imprecise. I'd like
The riders stayed
by three sarcophagi
but you lose gespreizt, which I'm sure you'd rather not. Nor do you want two extra beats.
You say there are three men in the tombs. The German doesn't specify. Folks isn't ideal (at all), but you may have other choices. Similarly, I'd like an equivalent to crone for Greis, instead of old man.
That's all - fine work as always IMO, which is hardly news.