It's great that you are helping your little brother with his homework. There are a lot of different ways that you can help your brother with his reading homework. For starters, help him better understand what he's learning by incorporating fun with learning. Try reading aloud with him, then have him try reading to you. If your brother is struggling to pronounce certain words, have him repeat after you and provide him with plenty of encouragement. Also, reading a bed time story together will help him become a better reader and listener.
I've included some activities and articles below to help you out. Good luck!
I think it's great that you are wanting to help your younger brother with his reading.
It's recommended with a 5 year old (Kindergarten level) to first to do a picture walk of the book. Point out who is the author (and what the author is) and who is the illustrator (what the illustrator does). This means that you would just turn the pages and look at the pictures (at that age they get a lot of what is happening in the story by just looking at the pictures, also when struggling with a word, they will be able to use this skill to look for picture clues to help decode the word) sometimes there will be something indicated in the picture that wasn't mentioned in the actual sentences, this will be helpful when taking AR tests because they may actually ask a question that was only in the picture to check for the observance.
Next, read the book. Help him with words that he does not know, by having him try to sound the words out or figure out on his own by using clues from the pictures or given in the text.
Next, read the book again. This time, you will notice that he may recognize words that he didn't the first time (mostly from recent memory).
Next, read the book again. This reinforces all he just had learned.
Finally, discuss the book. Have him retell the story to you. You may guide him by asking questions "what was the setting in this book", "who was the main character", "was there a problem" and if so "how was the problem solved" end with "did you like this story" "would you recommend this story to someone else to read"
It's not unusual to spend 30 minutes to an hour a night doing this, but this is the way to create a good reader and reading should be done in this manner each school night. At other times, for fun reading, just read a book to him as you normally would do. I usually read 2 books in a row, the first as suggested to you and the 2nd book just for fun.
Read 3 times
It's wonderful that you are willing to help your brother, but you may want to pass some of this responsibility to a parent.