That's completely wrong. Blackbeard and his crew did nothing to Whitebeard. It was the fact that he was already dying of old age, illness, backstab, loss of face, and dozens of swords and bullets threw him that he finally died standing up. All that happened with Blackbeard was him getting hit once by Whitebeard and begging for his life. I'm so sick of people giving Blackbeard credit that he doesn't deserve.
Blackbeard ran away from Akainu with his entire crew, him and that same crew had no problem take the life of the world's strongest man Whitebeard.