Looking for advice to tell parents and family that I'm pregnant!?

[Amy]

So here's the deal. I am 5 weeks pregnant. Both my dad and my husband's dad have birthdays this week so we are wanting to tell them at their respective birthday celebrations. I always buy my dad KC Chiefs stuff, so I bought a pair of itty bitty Chiefs socks... I'm so excited.

Anyway, my question is about my sisters. They are 15 and 16, and we are fairly close for being 7 years apart in age. My prediciment is if I should tell them when I tell the rest of my family for two reasons. One, I think it would be kind of fun to try to plan something special to tell them (differently from finding out when Dad opens his present). Two, because part of me is a bit worried about them being able to keep it a secret for now as they probably don't understand how worrisome I can be at times about if the baby is going to be ok, especially since I haven't had my first doc appointment yet. But, I don't want to them to feel left out by not telling them!