... would be Ram calling. I'll answer it.( the meaning of would and in which tense its used here ?)

2. "The guy on the phone had southern accent."
"That would be Tom."
(the meaning of would and in which tense would is used? Can we use other modals in the place of would ?)

3."We saw a police helicopter overhead yesterday morning."
"Really? They would have been looking for those bank robbers." (the meaning of would and in which tense its used here? ,does meaning change if i say " They may/might/could/must have been looking.........robbers.)

4.You would have to say/do that. (why would is used here ? What happens in meaning, if 'would' is removed?)

5.john said he didn't steal money.| well, he would, wouldn't he ? (why would is used here an in what sense?)

Why 'would' is used in those 1,2,3 sentences to mean "presumption" instead of using other 'must', 'may', 'could', or 'might'? Can we use 'may', 'might', and 'could', 'must' in the place of 'would' without changing the meaning of sentences ? I'd be greatfull if you could answer me. Thanks in advance