I'm gonna tell my oldest who is 17 soon. I feel like he'll need some time to adjust to the idea that he wont be here. (He's going away for college in the fall). Dh and I have agreed that we will tell him first because if we tell them all at the same time, he might feel upset about how excited his siblings are. I know he'll be happy about having another sibling, but also upset that he'll be a few hours away. Only a few hours but it feels like so long away! I'm super bummed he wont be here all the time either but we're going to make plenty of arrangements for him to see his baby sister/brother.
The others, who are 14, 5 and 3, I will tell at 12 weeks at least. I want to have an ultrasound first and make sure everything is going well. Family and friends will have to wait until then too!