AITA for not asking my Sister about my nephews birthday plans before sending invites for my son's birthday?

AITA for not asking my Sister about my nephews birthday plans before sending invites to my son's birthday?

I recently texted out an invitation to my son's third birthday to family and friends. My family all responded that they would come except for my sister. She texted back many hours later saying "we will be celebrating ________ But have fun". For context my nephews birthday is the day after my son's. I decided to schedule my son's birthday the weekend before the actual day because it was closer than the weekend after. Honestly I hadn't heard anything about my nephews birthday (he is turning 15) and It wasn't on my radar. I forgot it was the day after so did not think to reach out. Had she reached out to me I would have been happy to talk it through and decide what makes sense. The birthdays are a month out. I tend to plan ahead, my family tends to pull something together last minute. My sister is upset that I didn't contact her before sending out invites. She called my mom about being upset and my mom called me upset that we didnt talk about it before I sent invites out, more so putting it on me because I sent the invite out. My mom told me "it puts us and your grandparents in a tough place because now we have to choose." My grandparents have not communicated any concern to me. I can see how I could be the asshole for not thinking to collaborate, but also...there are two weekends on either side of the week of their birthdays...also two days in the weekend. I feel like maybe there were other solutions than to have it the same day.

If you're wondering what my relationship with my sister is like, it is strained. We haven't been talking much lately because she did some serious damage recently during an argument, and I have not been reaching out much because it always opens me up to doing something wrong and her lashing out brutally. My parents try not to take sides, which also ends up with them excusing her intentionally harmful behavior.

My husband feels like they shouldn't be blaming me, but when it comes to my family I have a hard time telling what is reasonable and what is not. The emotional regulation/support in our family dynamic is unhealthy. I moved a couple hours away in my mid 20s and have experienced different healthier dynamics, but when it comes to them I am still confused as ever. Logically I know what I'd do if it was anyone else, but with them I feel wrong no matter what I do.

So I humbly ask you for your thoughts.

p.s. Yes I'm in therapy, I'm still working on it.