Combining multiple neural networks with different activation functions
As you are trying to average out the values, and given the three have different domains, it makes sense to bring all in same domain before averaging out. You can normalize P2 (tanh) to 0-1 and then average the values.

If you want to try another way, you can combine these three networks and take the three outputs p1, p2, and p3 and input it to some more dense layers and finally predict the single output. This way instead of averaging out, you are bringing in some nonlinearity which will be helpful to learn the task.