Hi,
I believe your has depression features and irrational belief about the responsibility or having kid.
Kindly take take to an psychologist or counselor first for assessment and counselling.
Assure him that consulting psychologist is not an sign of weakness or mental illness.
Talking session can bring an difference in him.
Next Steps
proceed with family discussion( let your parents and their parents) and then move to counselling from expert.
Health Tips
1.show is unconditional love and affection.
2. Can ask his friends to talk with him
3. find what is triggering him not to have kid.