I agree with Karin in that if they are working with you, in spite of being over-scheduled & high-stressed, at least they are getting some time in for exercise.
Is it the sort of thing where they are just going through a busy time at work and home? If this is the case, then maybe the can fit in time when things quiet down. If not, would it be possible encourage them to think about some sort of long-term plan to cultivate time for themselves? This may be something you could work on together. Starting out, this may be just a few minutes outside of the sessions you have together. For example, your client may take a break from work to go for a short walk.