If the fighting is intense you really must separate your budgies.
In some budgies, the aggressiveness can come more to surface during breeding time due to the out of control hormones.
A good pair who is physically and mentally prepared for breeding (has the right temperament) will not exhibit violence towards their respective mate.
RIP sweet Tito (Summer 2008 - January 17th 2013).
You are missed and never will be forgotten.