"They are not visiting their parents."

Translation: Oni nie odwiedzają ich rodziców.

[luless]

Oni nie odwiedzają ich rodziców. - First 'they' is a different group of people than the second' their'. -> (As) are not visiting (Bs)' parents

[ngfio]

Yup, and "(As) are not visiting (As)' parents" would be "Oni nie odwiedzają swoich rodziców".

[Mel437497]

Sorry, can you please remind me which case "rodziców" is in? And how does it look in other cases?

[alik1989]

Genitive.

https://en.wiktionary.org/wiki/rodzic#Declension

[Jeremiasz185796]

Isnt it "oni" and not "one"

[Jellei]

It's both.

"oni" = there is at least one man among 'them'.

"one" = there are no men among 'them'.

[deactivated user]

Is the 'ich' necessary here? I wonder because it wasn't so in a previous question in this lesson.

[Jellei]

It shouldn't be necessary. Also, "swoich" is a lot more probable than "ich". But it hasn't been introduced yet at this point in this course.

"swoich" would mean that it's about their own parents.

"ich" is... well, about some other "their" parents.

Added the option to not use any possessive, it's natural and it will be understood that it's about their own parents.