The phrase 'believable characters' is correct and can be used in written English.
For example: I think that a good book must have believable characters with whom readers can relate.
Indeed, sophisticated criminals invest months in creating believable characters.
In general, look for texts with well-rounded, believable characters.
Believable characters form the foundation for flights of fantasy.
You have a real aptitude for populating your illustrations with believable characters.
The strength of BioWare's games has always been their believable characters and dramatic story lines.
Although the cast creates seven believable characters, the production feels unpolished.
It also led to the creation of more rounded, believable characters.
Their criticisms have merit, especially about the lack of believable characters.
His skillfully sustained use of Bangladeshi idiom combines with a surprising plot and wholly believable characters.
There are no laughs, no insights, no believable characters and no interesting story.
She is also one of the funniest, cleverest and somehow most believable characters ever.
