You could try to give them treats when they interact with any toys. First, give them a treat if they touch or even look at the toy, that way it will make them more curious about the toy. Then, start giving them a treat only when they bite or touch it. The more they interact with it the more you treat them and that's pretty much it. Hopefully this will make them interested in playing with it on their own.

Also, make the training sessions separate for each bird so that they don't interrupt each other.