"I'm having trouble figuring out what behavior is "normal" for my 4- and 8-year-old boys, what chores I can expect them to be able to perform, and what kinds of rewards and consequences work for the different ages. Is there a good book you can suggest? Or is that something I need to tailor for my own boys (i.e. figure it out on my own). I find that I am expecting things of my 4-year-old that his brother could have done at that age, because his brother was precocious. Or because I'm remembering it wrong!"
I don't know how many children you have, but I had a similar situation with my first two children. I would instruct my daughter to do something that my son was able to do at her age, and she wouldn't do it, or would have problems doing it correctly.
After a few weeks of frustration, I realized that I showed my son how to do everything, but hadn't necessarily shown my daughter how to do all the tasks prior to telling her to do them. I was being unfair to her. In my mind, I knew I had taught the chore before, I just forgot that I had to teach it to each child separately.
Even though she was a little older than I remembered my son being, I started over. I pre-taught every single chore for a while, before I gave her an instruction to do it. This was a huge thing for her! I praised her and had an enjoyable time working with her while pre-teaching, so she all of the sudden had a new found confidence and no more anxiety about my instructions.
It is OK to start the teaching over again, if the child doesn't seem to really "get it." There are some cases when the child isn't capable yet of doing a task, but usually if you pre-teach well, a regular child will be able to repeat your instructions.
Time-out should work for your four year old, but the eight year old should be at a stage where he earns extra chores, or looses privileges each time he chooses not to follow instructions, or accept your authority and judgement as a parent. (See Four Basics)
As far as the book goes, I don't know of a book that spells out what kinds of consequences and rewards would be appropriate for each age and kind of child. Make a list of what motivates them, and then you will probably find both of those things.
You really only need one consequence for common things, and three for the rule of three. (See post below)