At first you should create the account type for couples.

Then create the section for the profile questions that will be available to couples in Admin area > Users > Profile questions.

Then add questions.

Since the question should be available to couples only, check the box next to Couple in the For account type field.

Click Save

Let's take the sexual orientation question as an example.

Add a question for each member of the couple.

Choose the pages the question should be added to.

Click Save.

As a result, two questions will be listed in the Information on couples section.

If users fill this field it, the information will show on their profile page.