If my mother, father, brother, or sister felt the need to proselytize for Satan then I would pray for them, and if we magically transported back to the Middle Ages and the State condemned them to death I would weep and pray and regret their decision.
The Church does not, should not, and cannot execute people.
Your question also works for murders. If my loved one was a murderer and was sentenced to death I would be horrified and I would live the rest of my life in pain, but I would still support the death penalty for murderers.
Though, for the seventh or eighth time, I would not necessarily support executing heretics and blasphemers in today’s society.