Hi - if you had a 'show' (as we call it where I come from!), it might not be the full thing just yet, but possibly in a few days you'll get another one. I've just been through this with my sister and she had a show and had contractions for days before the real thing happened. The day before she had the baby she had another show (much larger and more mucusy, if you'll excuse the expression!), so it looked like the first one was just a small amount of it coming away.
With the first show, she went to the hospital, because the contractions were quite strong, and when they sent her home, she was about 5cm dilated, but still the baby wasn't coming and it was another 2 or 3 days before the second show and then the actual birth.
In my personal experience, things don't start to really happen until the contractions start and become so strong that you feel the need to go into hospital (for the pain relief more than anything!).
Sorry to hear that your in-laws might miss it all, but I suppose if they do, it'll encourage them to come out and see you again in a few months when the baby is safely here.
Good luck with it 