Don't think that vampires are just made up. In fact, you have to know that everyone has a blood-sucking gene, it just doesn't show up... Such as "leukemia" (... Please forgive me, this is the premise for me to start writing this...)
He needs his mother's blood to survive. Who can "protect" such a vulnerable life, and who can "end" it?
Is it the "brother-in-law" or the "vampire" who suddenly came...