Two pumps on the same pipe from the well is asking for trouble becuase they will almost certainly have two different characteristics and one will rob the other.
You have a holding tank. Holding tanks are often installed because the well has limited capacity. A better solution, if you want a separate irrigation pump, is as follows.
1. Well pump discharges to the holding tank, using a float switch in the holding tank as control. You should also have some kind of control to prevent the well pump from pumping the well below the inlet, which could damage the well pump.
2. The pump to your house, with suction from the holding tank, can work as is.
3. The irrigation pump can be connected to the holding tank. Since the water is supplied from the tank, the pumps won't "rob" each other. If you have a 2" outlet from the holding tank, you can connect both pumps to that pipe. You should have a full port ball valve on the suction side of each pump to permit one pump to be serviced while the other is still operating.
4. You should have "Safety float switches" in the tank as follows.
a. One at the lowest level from which you want to pump water, to lock out the house pump if the water gets too low. This protects the pump.
b. One at a higher level to prevent the irrigation pump from pumping you out of household water. This should be at a level that you want to maintain as a household reserve; not to be used for irrigation.