Hey lilac, I told all my parents around 3 months in. It was getting hard to hide it and I imagine some of my parents were suspecting it, however I wanted to be in the safer zone with pregnancy when i made the announcement and wanted to have my plan in place. I started with all my families in June-August 2010, so had been caring for their kids for 4-6 months. They were all really nervous when I first announced it but felt reassured right away when I told them the plan. Since being pregnany I have a family with a 11 month old who joined knowing exactly what was in the future for us.
Good luck and sorry for the late response, I really haven't had much time to browse the internet lately... taking more time to nap!