Newts and fish generally aren't mixed due to various reasons such as predation, different temp requirements, etc. The newts also secrete toxins which may not be good for the fish. As for the toad, the toad may eventually eat/attack the newt (which will also be stressed with another predator in the tank). Plus they both secrete different toxins which may affect each other. So I'd say no to the toad and to rethink keeping the newts with the fish.