Couples present subtle and complex sleep issues. Of course there are problems with one lark and one owl, as well as with couples on different shifts. Some couples begin sleeping apart when instead they might have been able to work out a win win together situation. Others will insist on same bed togetherness no matter what, even if both lives are impaired by fatigue.
I usually evaluate each separately to identify personalized sleep rest issues, and then meet together to work out Plan A. We consider room temperature, mattress preference, sexual and nonsexual as well as competitive interactions, complaining styles, and false assumptions about each other. We aim for a set of rituals that are mutually acceptable as the evening wears on toward bedtime, trying to substitute reality testing and science for impressions and impulses.