How to tell people who have experienced loss?

We're planning to tell our families that we're pregnant tomorrow! I'm wondering how we should go about telling my brother and sister-in-law. They had a miscarriage a couple years ago when they weren't trying to get pregnant, and then had a miscarriage earlier this year when they were trying. I believe they are still trying to get pregnant.

I'm wondering if I should text her today and give her a heads-up so they're not stuck having to pretend to be happy for us in front of others. My husband thinks it'll be okay and says they'll be happy for us (which I know they will be!), but I feel like I'd rather be safe and tell them.

Would love some insight into what you would do!