FAMILY.PY | OOPython
My one improvement would be this line of code

if self.death is None:
    family_tree.deaths.append('N/A')
else:
    family_tree.deaths.append(self.death)


can be reduced to one line:

family_tree.deaths.append('N/A' if self.death is None else self.death)


Also, I would recommend keeping all code not in these classes in a main guard, so you can import these classes without also running the code in the module.