A) "Below the bridge, the fishermen started shouting that if Chaudhary were to jump, they would catch him and foil his attempt to end his life."
In general, the "BE to Verb" expression when used in a conditional (as in #A), it merely serves to reinforce the remote modality that the writer wants to express in that sentence.
That is, for your example, the narrator thinks it doubtful that Chaundhary would actually jump, and that doubt is often expressed by using a past-tense verb form instead of a normal present-tense verb. This means that, usually, #A would have the same meaning as the version in your #3:
- 3.a "… If Chaudhary jumped they would catch him …"
BUT since your example sounds like an excerpt from fiction prose that is using past-tense narrative mode (that is, past-tense verbs are used to describe a currently unfolding scene to the reader), that #3a version would most likely be interpreted as an open conditional (not a remote conditional as the author had wanted). That is, the reader would interpret the #3a version in their imagination as though it was saying:
- 3.b "… If Chaudhary jumps they would catch him …"
which is something that the author did not want the reader to do. For the author wants the reader to understand that the narrator thinks it doubtful that Chaundhary would actually jump -- that is, that the possibility of Chaundhary jumping is modally remote.
And so, that might be a reason why the author chose to use the "BE to Verb" construction here ("if Chaudhary were to jump") instead of the past-tense verb version that used "jumped".
As to your questions #1 and #2: The writer might have used the irrealis "were" here to make sure that the modal remoteness use is easily and immediately understood by the reader as they are reading the sentence -- because this sentence is in fiction prose that is using past-tense narrative mode and so basically the same problem that I mentioned earlier comes up again.
That is, both "were to" (using the irrealis "were") and "was to" (using a past-tense verb) would usually be interchangeable in a sentence structured similar to yours, but that would be if the sentence was in non-fiction text. Since this sentence is in past-tense narrative mode, the reader, as they are reading, would probably interpret something like:
- [x] that if Chaudhary was to jump ...
- [y] that if Chaudhary is to jump ...
as they imagine the scene unfolding in their imagination. The problem with version [y] is that it is using a present-tense verb ("is") and that gives the construction a meaning that often suggests a sense of purpose, e.g. if Tom is to jump on time, then he'd better start climbing that ladder now. But that is not the sense of meaning that the author wants to communicate here, even though the reader will probably easily correct themselves as to the desired meaning by the time they've read the whole sentence.
This is one of the grammatical differences between the present-tense verb versions and the past-tense verb versions of the construction "BE to Verb". That, generally, when in a conditional construction, a present-tense version (e.g. is to Verb) suggests purpose, while a past-tense version (e.g. was to Verb) reinforces the remote modality.
(Note that your #B and #C versions don't have the "BE to Verb" in a conditional. And so, they will probably be satisfactorily answered by the usual grammar books.)