How to split a single CSV to multiple ones using different headers in the end results

I have this problem one of my clients wants me to split a spreadsheet I have been sending him for a long time into 3 separate sheets, that is

I regularly sent a file called A.csv with headers head1, head2, head 3, head4 ..... head25

Now he needs instead of just the A.csv file

B.csv head1, head14
C.csv head4, head5, head6, head7, head10
D.csv head3, head14,head15
(This is just an example, no relation with the real one, but the method to solve this should be the same)
In fact I need just to copy the columns and split the original sheet into the 3 separate ones, using just the columns he wants for each case. I have no clue about how to do this, the thing is I tried concatenating all into a single column with separated values, but I have some cells that have commas in the content, so I am open to suggestions. Another problem is the fact that the CSVs are really long sometimes 10s of thousands of products. I know programming, but what I never did is to program within Excel, so I don't know the syntax nor the commands.