Lowering the car is always gonna help the handling in some way or another, as it lowers the cars centre of gravity, reduces the body roll and makes the can more stable under heavy braking.

However you can go to low and totally destroy the car's handling all together. I would say 40mm is plenty low enough, much lower and you might start having problems with rubbing wheels and speed humps.

Tell you're bro to get his tracking done once the car is lowered, as this is a mistake i made and about 6 wks after lowering my car the brand new set of tyres on the front needed to be replaced