For instance I am using 4 blood knights
Having 4 identical characters is to ask for trouble.
Conventional wisdom says you should have a balanced party. It even says so in the manual on page 18:
"
However, Divinity: Original Sin is a party-based game with turn-based combat, so it is a good idea to build a party that covers many talents. A party with only fighter-type characters or a party with only wizards may be possible, but is not recommended for first-time players.
"
