Theophylact of Ohrid

He also foretells to them a worse evil, that they should suffer persecution from their relations. Wherefore there follows: Now the brother shall betray the brother to death, and the father the son; and children shall rise up against their parents, and shall cause them to be put to death; and ye shall be hated of all men for my name's sake.

Catena Aurea by Aquinas ↗

Gregory the Dialogist

"But you will be betrayed by parents and brothers, and relatives and friends, and they will put some of you to death." Evils inflicted by strangers cause lesser pain. But those torments rage more fiercely within us which we suffer from those in whose minds we had confidence, because along with bodily harm, the evils of lost love torment us. …

Forty Gospel Homilies, Homily 35 ↗

Bede

Brother will betray brother to death, and a father his child; and children will rise against parents and have them put to death. And you will be hated by all because of my name. But, etc. We have often seen this happen in persecutions, and there is no loyal affection among those who have different faiths.

On the Gospel of Mark ↗