(4) If john had told me last Thursday I

If john had told me last Thursday I will have given him the money but now it is too late.
An old man in the crowed warned Julius Caesar from the danger of death on a certain day.

Are the above sentence are correct?

If John had told me last Thursday, I would have given him the money, but now it is too late.
An old man in the crowd warned Julius Caesar about the danger of death on a certain day.

Why is “from” wrong here?

Simply the wrong definition.
‘About’ or ‘of’ are both correct.

“from” can be used instead of “in”, in my opinion.

An old man from the crowd warned Julius Caesar about the danger of death on a certain day.

Right?

Thanks

Neither ‘from’ nor ‘in’ are correct in the original sentence, regardless of your opinion.

I have already said that ‘about’ and ‘of’ are correct.