Fucking hell that's horrific about your Dad.
From the looks of it your brothers got your Dad's 'bad DNA' & you've gotten you mothers.
I know its pseudo science, but I've noticed in my own family that traits/flaws are more prevelant in certain members.
Keep on loving your mum, but wishing cancer & death is dark thoughts you don't need..
It's mothers day tomorrow & sadly I lost mine when I was young. So make it count mate.