Long long long story short - My dad has been with his wife for 20+ years in which I have not seen/spoken to her since I was of primary school age. I'm now 31 years old.
From what I know this is because she believed myself and my two brothers received preferential treatment to her two daughters (not my dad's daughters). My dad's wife excluded herself from my our side of the family and did not allow me and my brothers to meet our two half siblings she and my dad went on to have until their teenage years.
From what I have heard, my dads wife finds it difficult to keep friends, has fallen out with her own two daughters multiple times and currently one of her daughters refuses to even be in the same room as her due to her own personal reasons.
It's also important to note that myself and two brothers were never invited to my dad and his wife's wedding.
AIBU to not want her there on my big day? My dad had asked that she is invited to 'keep the peace' in his home and even offered the money to pay for her 'per head' cost on the day.