You need to recite one million OM MANI PADME HUM mantras urgently, not just to purify your negative karma but also to purify the negative karma of those who killed the monk and the whole family. Recite OM MANI PADME HUM without a distracted mind.
Visualize the Thousand-arm Chenrezig, huge like a mountain and radiating light. From Chenrezig beams of compassion are sent out to those family members who killed the monk, to yourself and to all your family. That’s the main thing. At the end of each mala think that the beams purify all sentient beings: the numberless hell beings, numberless hungry ghosts, numberless animals, numberless humans, numberless suras and asuras. They all become Chenrezig, including your family members.
As you recite OM MANI PADME HUM, mainly concentrate on your family. Beams are continually emitted from Chenrezig purifying them. At the end of each mala think that all sentient beings are purified and become Chenrezig. Again do purification and continue like that.
If you can, build a statue of Thousand-arm Chenrezig for the monk and those who killed the monk, for the rest of the family and for all sentient beings. The size of the statue should be 32 inches (80 cm).
My mother used to do 50,000 Chenrezig mantras a day but when she was close to dying, one year before she died, she said she couldn’t do that much. Because she recited all those OM MANI PADME HUM mantras she had more compassion than me, though she couldn’t read even one letter because she didn’t know the Tibetan alphabet.
With much love and prayers...