It's completely normal for subsequent babies to not engage until just before labour starts or sometimes not even until labour has started. They generally have more room in there with everything already being stretched that they can move up an down quite easily. But the chances of baby being born on or by the due date is no greater than any other woman - I know it's hard when you've been a few days early before, but it's also just as likely that you will even go past 40wks. Baby being engaged or not won't affect this.