When to tell family you’re pregnant?

I just found out that I’m pregnant and am trying to figure out when my husband and I should tell our families. Just for clarity, we will only be telling our parents, siblings, and grandparents-we will be waiting to publicly announce until the end of the first trimester. Doctor confirmed pregnancy and is estimating I am 6 weeks, but we will not have an ultrasound until 5/10. We are so torn of when to tell our families, because we want to share our excitement but want to make sure that we have a healthy pregnancy. Here’s where it gets even more complicated. My sister and I do not have the best history of getting along-long story short, she has always put me down, bullied me, and made every moment that should have been special for me about her (I’m talking my graduation, the day I got engaged, and even my wedding day). I had originally thought about telling our families on 5/11 after we get our ultrasound. However, my sister has just planned on having her engagement party that day and I am trying to be respectful (and not take away from her day). Unfortunately the next weekend is impossible, because me and my husband will have different days off from wthat week and his family lives several hours away. Would you tell everyone the day of the ultrasound (5/10)? Tell them before the ultrasound? Or wait until 5/25 (which feels so far away)? Any advice is appreciated!