When I first put them in my tank, they almost immediately kicked my cleaner shrimp (AKA Red Stripe) out of his normal spot in the branch type live rock. Then they beat Red Stripe up pretty good, they clipped his feelers and amputated a leg. But, shrimp are amazing and everything grew back when he shed his extoskeleton. Since then, they have left him alone.
As far as their agression to fish, if fish get to close they swat at them. I have not seen them actually make contact with any of the fish. I bought the pair together. My husband thought I was crazy. They wanted $8 for 1 or the pair for $20. He didn't understand why a pair should cost $4 extra dollars. But they are really cool to watch and now this whole egg thing is really neat. The female is almost twice the size as the male. Sometimes I see the female collect the pelets and bring them to the male. She actually turns him around and they spit the pelets back and forth while hugging.
I really don't have any advice for you as far as how to mate a pair. Like I said, I purchased them already mated. Do you live in South Florida? If you do, I can give you the info on the store I bought them from.
Thank you for the info on the eggs. I am sad that they are destined to become fish food. Do you think if I put her in a tank without a filter, only a bubler, any of the fry will survive?