I removed something, because I obviously misunderstood.

On the other side:
Why do you display 4 columns if you only use and allow two columns to be filled?
Why don't you ask before about the situation: Is it padre/madre, padre/padre or madre/madre?

Then you display only two columns with the correct headers which you taylor with an IF statement.

It is really less confusing for  the respondents

Like this
 

 

Or you ask the composition with a multiple question and use the plugin "hideEmptyColumn" to display the two relevant columns.

But, of course, up to you. It is your survey design.

Joffm