Student or Learner
a. I have received six calls from John and Harry.
Does that mean
1. All in all they have given me six calls.
2. Each of them has given me six calls.
3. Could be either (1) or (2). The sentences is ambiguous.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.
These would be clearer:
I have received six calls each from John and Harry.
I have received a total of six calls from John and Harry.
I am not a teacher.