It’s helpful to always write a short background on the characters. Who are their parents, where did they go to school, what are their hobbies. What do they like what don’t they like? That way you aren’t just creating an extra diverse character but an actual person. It’s important to keep in mind that their ethnicity is part of them but it doesn’t complete them, they’re more than that. It’s however important to maybe look up usual habits and dos/fonts within these particular cultures so that you properly represent them.
Sorry if this doesn’t really help, but you can always send me a description of them and I’ll see how I can help