AITA to feel hurt and not being included on my niece’s bday

I (27F) have two older have siblings, 38F and 41M. I lived with them until my parents divorced when I was 6. Following that, they lived with my dad for a short time before moving to England. I didn’t get to see them much and we definitely aren’t close. I often wonder if the fact that they didn’t end on good terms with my mum has in some way negative affected our relationship but I digress…

My sister is visiting with her 3 children and it is her middle child’s birthday today. They said I was welcome to join them for dinner- I was hoping to be able to spend more time with them saying as I rarely see them. They spent the day in the city centre not far from where I live and went to an escape room attraction.

I get that my sister might have just wanted to spend time with her kids, but I still feel left out. When I’ve expressed feeling like this in the past its been made out that I‘m never happy with anything and am just spoilt as I’m the youngest child. So… am I being unreasonable? AITA?