The therapist told the couple

[Bassim]

I am wondering if my sentence sounds natural.

The therapist told the couple they have to focus on maintaining good relationships with each other or they risk separation.

 

[teechar]

I am wondering if my sentence sounds natural.

The therapist told the couple [STRIKE]they have[/STRIKE] to focus on [STRIKE]maintaining good[/STRIKE] (saving) their relationship [STRIKE]with each other[/STRIKE] or (else) they risked separation.

Consider using "advised" instead of "told."