My advice on this topic is to keep the characters key characteristics in mind when you try to write them. And also study how others write them to get some idea of their personality. Of course, this is easier with characters that get a lot of screen time, but it's possible with characters who get little screen time as well.

For example, when I wrote Genichirou for the first time, I went and read a bunch of fics from his POV to better understand how others perceived his character (I also asked people who had written him, what they thought of him but you don't HAVE to do that).

And as for Bram, there's not at all a lot of content for him, so for my fics that include him, I think about what his key traits are/could be (quiet, blunt, internal thinker) and then try to place them to whatever scenario I am writing him for.

Keep in mind though, that your perception of a character will be different to someone else's, and that's okay, because we all experience things differently!! Just write what you want to write, and if you are truly worried, you can always ask a friend to read over your work :)

Hope this helps!! I'm not the best at giving advice haaaaaaa 😅