In the Early Middle Ages, it was common for family members to murder each other to secure power but by the end of the Early Modern Period, it seems to have become less frequent.
Ok so we will have to differentiate the degree of family, because the royal houses of europe married each other continuously for centuries.
in England the Plantagenets were masters of family murders. The century long war that put the Tudors on the throne was waged with Plantagenets on both sides, the Yorks and the Lancasters. the throne alternated cousins, uncles, and so on killed each other for years.
Probably the most brutal and callous murder when Edward II's wife Isabella of France came home from exile, brought an army, and had taken her husband's bitterest enemy Roger Mortimer as a lover. Not only did they depose him, they hung, drew, and quartered his gay lover and while alive, castrated him and put it his mouth, again while alive (they say he was silent the entire time, even during castration, and only started screaming when he saw his entrails being pulled out), she murdered Edward several years later allegedly by buggering him to death with a white hot sword. The nickname shes known by now is the "She-Wolf of France".
It later culminated with one of the most famous murders committed in the Tower of London when a politically maneuvering Richard III made his final power grab and killed his 10 and 12 year old nephews by smothering them. The kids had been the rightful heir to his favorite brother and removing them made him the rightful king. Family killing in England slowed down after Elizabeth I's death. Her older sister (Bloody) Mary I had made attempts to get to her, and when she finally died and Elizabeth took the throne, she executed her cousin Mary, Queen Scots. After that there were many times close family deposed eachother, but it stopped all together with the arrival of the Hanover King George I in the 1700's. Those are the ones im sure of, im not for sure as far as mainland europe. Actually, closer to recent times in the aftermath of the Russian Revolution that overthrew Tsar Nicholas II, George V had a chance to rescue the Tsar and his family from certain massacre at the hands of Lenin and the Bolsheviks, but ultimately refused because of popular opinion against Russians. The Tsar was his first cousin, looked almost identical to him, and were the closest of friends growing up. So I'd go ahead and consder that family murder, though indirectly.