Hi,
so irony may be kidding when people are talking, but sarcasm will be more serious? Yes.Irony does not have to be personal comments, either.
eg It's puring with rain, and I say to my friend 'This is a good day for our picnic!' I'm expressing one meaning by saying the opposite.
can irony be like a thought of a person or someone narrates something?
Yes. It's not just words, it can be an 'idea' or 'thought'. It's like 'a meeting between opposites'.
eg Tom asks Mary to marry him. She refuses, because she loves money and Tom is very poor. She marries Fred, instead. The day after Mary's wedding to Fred, Tom wins ten million dollars in the lottery. That's ironic.
Best wishes, Clive