For #3, On Halloween, we dressed our almost 2 year old son (he is #2) as a BumbleBee and put a T-shirt I designed on him that said "I AM A BIG BROTHER TO BEE" and had a bee drawn on it :) It took a few seconds for everyone in the family to realize what it said and meant :) We all get together to trick or treat every year and we have 11 nieces and nephews.
For #2, we had all the family over for a usual monthly get together, made homemade pizzas and spelled out in sausage "Baby #2 is on the way" for everyone to see.
For #1, we were announcing during a family grab-bag. We put an extra wrapped gift on the table -- it was my ultrasound at about 9 weeks in a CD case and wrapped. My brother in law opened it, thought it was a CD for a few seconds then started staring at all the women in the room till we busted out laughing.
We try to make each announcement something fun :)
Good luck coming up with your own creative way!