Hello jasonandsusan,

You're on the right track... Males sing/croak and have a saggy gular. During mating season you may also notice a larger dark thumb pad called a nuptial pad on the males. Females are larger than males.

It could be that they are still young, you have two females, or they need more foliage in their home to feel safe.

At three years, they should be croaking. They general start croaking around 4 months out-of-the-water, up to a year for late bloomers.

Do you have any photos?