When to tell our parents!?

Hi!

I just had my first ultrasound today, which showed I am 5 weeks and 1 day along. This is my first pregnancy, so this is all new to me. Once I got pregnant I thought I would want to wait until I'm at least 8 or 9 weeks to tell my in-laws, then as it became more real I thought as soon as we hear the heartbeat. Since I'm less than 6 weeks, we didn't get to see/hear the heartbeat yet. This weekend is my in-laws 40th Wedding Anniversary and I am now thinking that it would be such a wonderful surprise to tell them when we get together to celebrate, but is it way too early? I'm really close with them and I want to share our excitement with them and I want to assume this will be a healthy full-term pregnancy, but I also understand that a lot can happen in the next few weeks/months. I don't want to tell them, then have to break sad news. Also, I would ask them not to tell anyone else until I'm 12 weeks, is it fair to ask them to keep quiet for 7 whole weeks!? My husband says he is fine with whatever I'm comfortable with doing. Would love advice.