A Westchester mom and her two young children — all slain by their deranged husband and father — were laid to rest yesterday as relatives struggled to make sense of the murder-suicide tragedy.

“How could this have happened? It can’t be real,” sobbed Gary Perez, whose daughter Amy, 46, and grandchildren Molly, 10, and Gregory, 8, fell victim to his son-in-law’s Sam Friedlander’s rage last Tuesday.

Perez crumpled in tears, unable to say the final kaddish, the Jewish prayer for the dead, at the funeral service in Bucks County, Pa., where Amy grew up.

“There are absolutely no words” to describe the “unspeakable grief,” shock, anger and “lack of justice,” Rabbi Craig Axler said to several hundred mourners at the Joseph Levine & Sons Funeral Home.

Sam Friedlander, 50, beat his wife to death with a piece of furniture, then blasted the children with a shotgun before taking is own life in the tony Cross River section of Lewisboro.