I think the main thing is that these people didn't care about why or what Ishid was trying to do but the fact that his fire was so powerful it quickly destroyed his mother's body,bones and all.The father on the other hand probably knew he couldn't control his power and didn't understand what he...
@mahtan I think she was killed because her sister (the saintness) framed her for things she didn't do but she was portrayed as the villainess so now she's going to become a bigger "villainess" and rip off the mask of her fake faintness sister.