Mixing species is not something that is acceptable. If someone was to mix species they would have to be very experienced in the husbandry of each species. Zoos for example mix dart frogs, but they also have staff members that are extremely qualified to attempt it and they are monitored very closely for signs of trouble. I recommend that you start with something a little easier to keep than dart frogs for a little while and then go for the darts. Every new dart keeper wants to mix all the pretty colors and put reptiles or newts in with them right away. Please listen to the advice that you already have been given and avoid a disaster that others have experienced and are trying to keep you from having. And dart frogs still have some toxins in their skin even when captive bred.