Any book recommendations that teach you how to make sure each character sounds different in dialogue and is recognizable even without dialogue tags? Any book tips to learn more about character development?
Dialogue (Elements Of Fiction Writing) by Lewis Turco is an older book from Writer's Digest Press (F+W Publications) but it is really good.
I honestly read it in a day (it's not too long) and it provides a lot of good detail about getting character voices right and keeping them consistent.
Our understanding of a character in a novel often comes almost entirely from the things they say and this book does a good job of helping you learn how to set that up.