Family wedding coming up! Do we announce before or after??

Here's my dilemma: my husband's sister is getting married at the end of the month. He has a lot of extended family, and we haven't told any of them yet (his immediate family knows). I don't want to overshadow her special day by announcing our pregnancy too close to the date... but I'm also worried I might be showing around then, and it might make sense to announce before the wedding. I'll be 16 weeks by then. I feel like if I ask my sister-in-law what would make more comfortable, she'll just be polite and tell us it doesn't matter. Does anyone have any advice? Thanks in advance ;)