Will Play Store update a SideLoaded APK We have created an android App, and we wish to share the APK with a few friends and family before publishing it to the Play Store. Our concern is that, if they install the APK, and then later we push an updated version to Play Store, even with the same signature, will the update be delivered to the users who downloaded the APK manually and installed it. 

Thanks
Nishith
As of 2015 Google Play will detect apps with the same signature, but they will not be updated unless the user un-installs the app, then reinstalls from the Play Store.
So in short, to answer your questions - no Google Play will not update the application if it is installed from somewhere other then the Play Store.

see:
https://stackoverflow.com/questions/14746330/android-sideloading-applications-and-keep-them-up-to-date-via-google-play#answer-28135853