Needs analysis is the basis for choosing content. Then, when you see they can barely take 2 hrs per day twice a week for the class, I recommend you push them for an additional 30 mins homework session -on their own-. I usually interrogate them about their lunchtime, workout and TV time. If they end up saying the spend 1 hr on any of these activities (or on each one) I demand that they take 10 mins from each one, to study outside class.
Of course, you don't want to impose things, be extra flexible, but take every opportunity to point out that if there's no progress, it's because they're not devoting enough time to practice and review. (I have taught around 3 couples under the scenario you're describing...)
Envolve them in the planning process. Design a course, with time allotments, final date to accomplish it and a deadline -I mean cut yourselves some slack, they're tooooo busy!-. if you tell them the goal to achieve, and make them self evaluate at the end, they will become aware of how well or not they're doing in their English classes.
I hope I shed some light on your question.
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