Partner has monotonous reading voice

My partner likes to read bedtime stories in a terrible sing song voice, I do my best to demonstrate a more normal way of speaking when I do it but he/she just rolls her/his eyes and leaves the room

I sometimes have to moderate myself at the school's weekly class reading day... as some of the parents don't have my ability to inhabit the characters and bring the story to life.

Is it ok to do all the characters in the same voice? I worry that when i'm doing certain people I slip into cultural and ethnic stereo-types.