Quote 1
"Who said anything about safe? 'Course he isn't safe. But he's good. He's the King, I tell you." (8.26)
Mr. Beaver distinguishes between being fundamentally good and being gentle or "safe" to be around. Aslan is good, but he's also terrible, awesome, and powerful. In this book, good is not going to just lie down and turn the other cheek. Well, OK, it is, but it's going to be pretty awe-inspiring at the same time.
Quote 2
"The reason there's no use looking," said Mr. Beaver, "is that we know already where he's gone!" Everyone stared in amazement. "Don't you understand?" said Mr. Beaver. "He's gone to her, to the White Witch. He has betrayed us all." (8.53)
Mr. Beaver isn't prejudiced by a family relationship to Edmund, and he's able to recognize right away that Edmund's sudden disappearance means trouble and danger.
Quote 3
"I didn't like to mention it before (he being your brother and all) but the moment I set eyes on that brother of yours I said to myself 'Treacherous.' He had the look of one who has been with the Witch and eaten her food. You can always tell them if you've lived long in Narnia, something about their eyes." (8.61)
Like most people in Narnia, Edmund wears his heart on his sleeve. OK, well, nobody falls in love here, but you know what we mean – he wears his thoughts on his face. Appearances are rarely deceptive in this world, and if Peter, Susan, and Lucy had known what to look for, they might also have realized what was happening to Edmund.