Looking on the internet deeply has found these results:

one should help their friends in difficulty is the most popular phrase on the web.

one should help his friend in difficulty 110 results on the web	one should help their friends in difficulty 1412,000,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
It doesn't look like this phrase is very popular! The search could not find any examples on the internet.	One should help only one's own kind. Jenny had the inspired idea putting Serena and Poppy Lifton and their friends in the front row. Only criminals and their friends in the West who wish it to be separate. You're one of those lean, hungry types that put the wind up Julius Caesar. Men who stab their friends in the back. The Molina Cartel and their friends in Al Qaeda. They miss their friends in Munich. We believe that Member States should help their own redundant workers. All I had to do was take a bag of cash out to some of their friends in North Shore.

one should help his friend in difficulty

110 results on the web

one should help their friends in difficulty

1412,000,000 results on the web

More popular!

It doesn't look like this phrase is very popular! The search could not find any examples on the internet.

One should help only one's own kind.
Jenny had the inspired idea putting Serena and Poppy Lifton and their friends in the front row.
Only criminals and their friends in the West who wish it to be separate.
You're one of those lean, hungry types that put the wind up Julius Caesar. Men who stab their friends in the back.
The Molina Cartel and their friends in Al Qaeda.
They miss their friends in Munich.
We believe that Member States should help their own redundant workers.
All I had to do was take a bag of cash out to some of their friends in North Shore.