Difference between "touching", "about" and "concerning" as a preposition

The Macmillan Dictionary regard touching as a formal preposition, and other dictionaries nearly related the prepositions concerning, about, touching as synonyms. So is it fine to use all of three prepositions in written exams, as in:

1. They had discussed touching the beauty of that place.




2. They had discussed about the beauty of that place.





3. They had discussed concerning the beauty of that place.

I don't have an idea which one is more preferable in written exams or other formal speaking occasions?

And the following usage of touching as a preposition lead me towards the confusion, as it looks like present progressive tense:

• It is touching them.

In this case, shouldn't it be like this:

• It is about them.

Answer

Notice how the example usage in Macmillan is not a complete sentence, and is preceded by a noun:

questions touching party politics or religion

whereas your example uses a verb before the word touching:

They had discussed touching the beauty of that place.

Therefore, a better example usage would be:

They had a discussion touching the beauty of that place.

Although, as another answer mentions, this isn't a common usage in contemporary English, and it is prone to sound a little awkward even when used grammatically.

One more common, contemporary phrasal verb is touch on. Macmillan says:

touch on something to mention something when you are talking or writing

So, one could say:

Their discussion touched on the beauty of that place.