Telling family

So I want to wait until 12 weeks or as close as possible to tell friends and family because that's probably when I'll get my first scan and I'll feel more sure of this. My fiancé is nervous to tell his parents as well until we can figure out if they're separating (his dad lives elsewhere every other week). But I'm really not wanting to tell my older sister, she tried to get pregnant for 5 years before she left her fiancé. She's living with her boyfriend now and they don't use protection and she's still not pregnant. I tried for over a year myself but I'm just super nervous to tell her because I know she'll be hurt by it even if she will love her niece/nephew (she loves her boyfriends nephew so I know she'd love my baby too). I just don't know what to do. I know I'd be upset if my younger sister had gotten pregnant first (partially because she's 16 and single). I need advice...