Pump size ???

My friend is building a 2000 sq ft home off grid. I had installed the alternative energy system he is currently using to provide electical power for his double wide trailer. Everything has been working great for over four years. I have a dual SW4024 system with three Hawker 24 volt 1600 amp battery banks. I plan on adding another 4kw inverter for the larger home. They currently use a generator to power the water pump. I want to install a dual pump system that will allow one pump to use the generator and or one to use 24 volt DC. I need advise on the best size pump that can provide 30 to 40 psi for running two showers running at the same time using 2 GPM shower heads and allow flushing the toilets at the same time. The water tank is 1500 gallons above ground. Can anyone help. The former Energy installer had sold the owner a Dankoff Flowlight 2920 pump which was never installed. I do not think it can handle the requirements. They are also wanting to install a swimming pool, anyone have any advise on a solar run filter pump system?

Many Thanks, captarcandspark