I wouldn't be surprised if the characters find Grant in the castle, actually, though they could go any # of ways with the show to include Grant and I think it would be a mistake to not do so. I'd make roughly the same estimation regarding Death. I'd be rather shocked if either of these were not included.
Tbh, I'm more curious about whether or not we will see any of the Curse of Darkness or Nocturne of Recollection characters. Those seem like far greater stretches, but I couldn't help but notice the small white flowers in the show (I only noticed them in one shot particularly, but my little sister said she saw them at Lisa's house; I need to re-watch the first episode to see if that's true). I don't know if it was intentional or not, but they reminded me of the radio drama, and the prophecies from the future are obvious references to Saint Germain and his kind, so it's not unthinkable that there might be more references to these in the series... actually, let me check and see right now. Edit: I don't see anything like them in the first episode, but about 6 minutes into the second episode, Trevor steps by these little white flowers:
https://68.media.tumblr.com/681abb4f58454ff0b53b0ad5b87bcdfb/tumblr_ot0qmwChvD1tl3y3go1_1280.jpgIt's probably just a coincidence, but worth mentioning.
Edit2: Forgot to mention. The old woman puts white lilies at Lisa's house. Mina holds a white lily in one of the artworks for Aria of Sorrow:
https://vignette2.wikia.nocookie.net/castlevania/images/8/87/AriaArtwork.jpg/revision/latest/scale-to-width-down/300?cb=20080227220819Edit3: The flowers in the show look a lot like the ones on this piece for Lament of Innocence:
https://s-media-cache-ak0.pinimg.com/736x/a2/b5/d2/a2b5d238e5184ad9b8d298b384c00f1f.jpg