1. WordPress Auto-Login:
This plug-in will let you setup autologin for your WordPress blog; meaning that if you have parent website with Login functionality and you want some of users based on some role/rights or login credentials to be able to login to your WordPress blog then you can do that with it. It's pretty simple you can specify multiple websites with different users for each of them.
It will help you setup central log-in system for your parent/friend website and your WordPress blog.