It’s really up to you. If you have a spine you’ll be reading to everyone, then just read that to everyone. Then I usually have older kids read most of their books themselves, unless I know all of us would really enjoy it, OR unless something is really very difficult (Shakespeare, or Plutarch, or something like that–a really challenging book) because that seems to be helped by reading aloud. I’ve found Parables of Nature to be another one that the children really enjoy if *I* read it, but do not like it if *they* read it themselves.
I love to read to my children, and I kind of miss reading more to the older ones. So every year I “claim” a few books so I have a good excuse to keep reading to them. 🙂