I have seen the first season of Tokyo Ghoul and a few episodes of Root A and I want to know if this is enough to read the Tokyo Ghoul RE manga. I have heard that Root A doesn't fit into the story of the manga, so should I watch it before I read RE or not? I'm also not sure if you can watch the first season of Tokyo Ghoul before RE, or do you have to read it in the manga?
Tokyo Ghoul: Root A heavily diverges from the original manga, which you've heard correctly. The first Tokyo Ghoul season does an okay job of covering its manga counterpart, but there are things that were skipped over or different. Since RE is the sequel to Tokyo Ghoul, if you go into it having only seen the two anime seasons, you'll be a little confused due to some of the plot points you'd have missed from the manga.
If you want to experience RE in full understanding, you might want to read the previous manga first. However, if you don't mind some confusion, it's ultimately up to you. Hope this helped!