Scenario:
A guy coming from a noble family commits a big sin. His mother says "I'm glad your father isn't alive today, how could he have tolerated all this. So glad he didn't have to see what disgrace you've brought this family to. Poor soul"
Question :
How do I put the conditional sentence here? If your father were alive today, he would've committed a suicide?
You don't commit a suicide--you commit suicide. (After all, there's only one possible suicide you could commit!)
But we'd probably say "If your father were alive today he'd kill himself."
One English idiom is, "to roll/turn over in one's grave", "Your father would be rolling over in his grave if he knew what you had done."
Or you could just say, "If your father were alive today, he would kill himself." There is nothing wrong with this sentence (although it may be unintentionally humorous).
The first conditional, "How could he have tolerated all this?", is grammatically correct (though it should end with a question mark, not a period).
But it's not quite what you want here, since "How could X have done Y?" means either (1) "I do not believe it is possible that X did Y" or (2) "I am interested to know the means by which X did Y."
Here are a couple of other options:
How would he have been able to tolerate all this?
He would not have been able to tolerate all this.
The second conditional, "He would've committed a suicide," is almost right.
The conditional structure is fine, but you "commit suicide", as @StoneyB said. However, this is has nothing to do with the fact that you can only commit suicide once! Rather, it's because "commit" + "type of crime" is always used like that. You "commit theft, commit arson, commit homicide" and so on.
Note that English-speaking cultures have no tradition of parents committing suicide over the behaviour of their children. If the story is set in another culture, it may be fine. Otherwise, @Andrew's suggestion is good: "He would be turning over in his grave." This is very idiomatic English. Another sentence that makes cultural sense, although it is not as idiomatic, is "He would disown you."
Finally, it's good that you're using colloquial phrases to make the dialogue more realistic. However, in a situation like this, where the mother is angry and talking about a serious subject, she would probably not say "So glad he didn't have to see," but the full sentence "I'm so glad he didn't have to see."
