You may be having a leak or bypass which is allowing more water to the sump than the pump is able to handle.

To find out ... shut off all pumps and see at what level the water level in the sump stabilizes. If the sump continue to receive water after the water level in the tank is at or below the outflow tube/pipe then you have a leak from the tank into the sump.

The level in the sump should be self regulating. If the sump overflows with the pumps off then either you have too much water in the system or water is draining into the sump from below the outflow level in the tank.

Hope this helps.

Mike