It's because MC told Lorcan's father that Lorcan's uncle is meeting at hotel with Lorcan's mother (which I assume they were cheating).
After that, Lorcan's father probably got too angry and killed his wife (or maybe there's another reason we don't know). As lorcan is still child, he don't know why his father did that, and he finally then blamed it to MC because the last thing he knows his father change after what MC told them.