Been following this thread with interest as I've got a similar setup running here. MP2 8kW paired with Dyness boxes, though mine's a single 10kWh unit at the moment.
The inrush current issue you're describing is classic – those power tools pull an absolute beast of a starting load. A 1kW skill saw can easily draw 3-4x rated power for the first 200-300ms when the motor's spinning up. Your Cerbo's probably seeing the voltage sag and getting twitchy about it.
Few things worth checking:
Battery side – make sure your Dyness DIP switches are set for your actual voltage config and that the BMS isn't limiting charge/discharge current too aggressively. Some folks don't realise the factory settings are quite conservative. Check if you're hitting any current limits when those tools kick in.
Inverter settings – your MP2 has configurable behaviour for low voltage events. In VEConfigure, look at the low battery disconnect settings and make sure the thresholds aren't too hair-trigger. You might also want to check your AC output current limit isn't set lower than needed for the startup surge.
Cable runs – sounds daft but worth confirming. What's your battery-to-inverter cable length and gauge? Even slight voltage drop compounds the inrush problem.
The Dyness boxes are generally solid but they're not forgiving of sharp transient loads without proper configuration. Have you got any system monitoring running? Would be useful to see actual voltage and current graphs during one of those tool starts.
What voltage sag are you actually seeing when the pump fires up? That might help narrow down whether it's a battery response issue or inverter configuration.