How to apply a modifier if the other modifier is being applied?

There is a requirement for 2 modifiers - one is discount & other is surcharge. Discount is for 2 different categories (Standard & Special). If customer orders equal to & above a fix quantity from single category or both, then it will get discounted price. Out of these, if it is from Special category, then 5% surcharge will be applied on top of the discounted price. If customer orders less than fix quantity, then there won't be any discount / surcharge. We tried to use bucket. It is working fine, if quantity is equal to or above the fixed. But,