I'd go ahead with your plans.
Devin, seeing as the end of July is only two weeks away, and you are only 8 weeks now, I would let your sister have her time in the spotlight before you announce. We waited to announce until nearly 13 weeks, and I think a lot of people announce after the first trimester is ended.
If you announce at 12-13 weeks, your sister would have a few weeks to "shine" before you announced, and I think that would be really kind of you, given you've been in the position to be "outshone" before.
That's what I would do, anyway!
I think you have your answer....I was going to say that I agree with Adrienne, because I think you should wait, but if you are starting to show and you know people are going to notice, then I would just tell people after your U/S.
I think that is good logic, Devin! I guess it is hard being SOOO thin--I am thin but I've always had a bit of a round stomach and I honestly think if I wanted to hide it until NOW I might have been able to!
But yeah, hopefully you can tell after the u/s and she'll still be a few weeks away from giving birth!
GL with your decision! I think your "go with the flow" logic will work well.
I also wanted to share my experience with a similar situation. DH has a younger sister and younger brother. His brother had the first grandchild and Selin is the second. Everyone in the family had pretty much given up hope that