So it's sounding like S is the problem? Have you considered dropping S's sleep during the day and still keeping to the normal night time routine and putting S to bed 30mins later?
Our boys sleep in the same room and we had to drop DS2's day time sleep and put them to bed at different times to make it work. So DS2 goes to bed at 7pm and DS1 at 7:30pm.
We read their stories in a quiet place out of their bedroom. Then teeth, toilet and bed.