Snipp, Snapp, Snurr (triplet boys) and Flicka, Ricka, Dicka (triplet girls) are sweet and good morals — they work hard, make mistakes, fix them. Billy & Blaze?? There are some nice “I Can Read” or “Step Into Reading” level books that are history based.
Step Into Reading step 2 or 3 would be good: Balto and Christopher Columbus are both step 2, one about Whales: Gentle Giants, I think; Pompeii…Buried Alive and there’s one a little Mexican vilage where a little volcano began — those might be the next level,Titanic Lost & Found and Sea of Ice which are higher up and more text, longer paragraphs, etc.
“An I Can Read Book” has a different level system, but there’s lots of good ones at level, but look through the stacks at your library to see what’s a good fit: Daniel’s Duck, Sam the Minuteman, The Drinking Gourd, Clipper Ship, etc. (Frog & Toad are at level 2 in this series.) There are actually lots of good ones (more than I expected as I am not typically a fan of early readers in terms of content, but I’ve found that the ones that are a bit more historical in nature are more tolerable and definitely help fill the need of building fluency while still giving them something interesting to read about.