It sounds like they are at the age where you can start the transition to their reading more of their books independently, yes. Charlotte started making that transition when the children were about 10 years old. She mentioned a couple of great reasons for encouraging the students to read independently: 1) They will see how the words/names are spelled; and 2) They will develop the habit of self-educating.
So, yes, I agree that if the boys can read comfortably on their own, this would be a great time to start making the transition a little at a time. However, if either of them is struggling with reading, I would hold off or take really tiny baby-steps toward the transition to independent reading.