I don't want to eat at the table with my family on my aunt's birthday
Why don't you want to eat with your family at this table on her birthday?
I'm not keen on eating with my family.
Your family is counting on you to eat with them, so go ahead and eat there anyways. You will feel better you did a good deed for the day and your Aunt will feel good about it too.
No, I'm going to leave the dinner early.
You should be mentally present with your family when you all spend time together. Taking part in family events will only help to stregthen your bond.