You will find this information in the Epilogue. A Jeep in which the girls are riding is being followed by the "calies." It forces them off the road.
The girls are forced out and being led to a car, but Patria breaks away long enough to shout to a passing truck, "Tell the Mirabel family in Salcedo that the calies are going to kills us!" She is summarily dragged back to the car. The driver of the car reports the murders back to Dede as he was asked to do.
Patria is correct. Dede describes the carnage: "I didn't want to hear how they did it. I saw the marks on Minerva's throat; fingerprints sure as day on Mate's pale neck. They also clubbed them...
Their mother is of course upset. She learns to deal with her grief by doting on the grandchildren.
As for the summaries, you can find those by following the link below.