Dovii are usually pretty easy to sex. I have had a 4" female spawn so they'll probably be sexable. Females are smaller and don't have much of a nuchal hump and males are larger and have more blue on their fins.
You should wait until they pair off on their own though, instead of just throwing a male in with a female. There is usually alot of conspecific aggression with dovii though, so you'll have to watch out for that.