I need two quotes each from Of Mice and Men about Candy's and Crooks's weakness.
We can find lots of quotes to support the idea that Candy is weak. In Chapter 3, for example, Candy is unable to shoot his lame dog. Instead, he hands the dog over to Slim, proving that he is not strong enough to end the dog's misery himself:
At last Candy said softly and hopelessly, "Awright—take 'im."
Secondly, after Candy's dog is shot, we have another example of weakness. This time, Candy is talking about himself and how his physical weakness—caused by old age— will soon prevent him from being able to financially support himself:
"I wisht somebody'd shoot me."
To find quotes about Crooks' weakness, take a look at Chapter 4. Because of the injury to Crooks' back, physical weakness is a problem for Crooks, as we see in this quote:
And he had thin, pain-tightened lips which were lighter than his face.
It is clear, then, that Crooks spends much of his daily life in pain.
What we also find with Crooks is that because of his skin color, he feels weak. Specifically, he is not valued by anyone else on the ranch and has become socially isolated. This is shown clearly when Crooks is having a conversation with Lennie:
"If I say something, why it's just a nigger sayin' it."
Crooks, therefore, is weakened because of the prejudice and discrimination that he experiences on the ranch.
Here is a quote said by Candy, after his dog is shot:
"When they can't use me here I wisht somebody’d shoot me. But they won’t do nothing like that. I won’t have no place to go, an’ I can’t get no more jobs.”
Candy feels like his days are numbered. He is weak because his not a complete man, and if he can't work on the farm, he can't make money. There will be no way to survive.
This is a quote by Crooks to George:
“You got George. You know he’s goin’ to come back. S’pose you didn’t have nobody. Sure you could play horseshoes till it got dark, but then you got to read books. Books ain’t no good. A guy needs somebody - to be near him.” He whined, “A guy goes nuts if he ain’t got nobody. . . . a guy gets too lonely an’ he gets sick.”
Crooks feels weak because he doesn't have a buddy, someone to watch out for him or just to pal around with. He is lonely and unprotected.
This following quote emphasizes that he is unprotected:
“Nigger, I could have you strung up on a tree so easy it ain’t even funny.”
Curley's wife says this. She is underlining the fact that Crooks is always on eggshells, never knowing when someone will come after him.