Your intention is to connect several turbines in series to produce electricity in the same pressure pipe of a dam. In fact, it makes no sense.
Hydraulic turbines operate based on head and flow. We call the height between the dam water surface and the waste water surface the head.
For an idealized hydraulic turbine, the power it can emit = flow × head (simplified formula). If the height difference is 60 m, if two hydraulic turbines are connected in series in the pressure pipeline, the height difference of each turbine will be reduced by half while the flow rate remains unchanged, and the power it can produce will be reduced by half. In addition to complicating equipment, increasing equipment investments and making management more difficult, what is the point?
With regard to the installation of several pressure pipes inthe same dam and the operation of several generators in parallel, this is a common practice in most hydroelectric power stations.