My mother is taking on the Father of the Bride duties and giving me away as I have no father. I am unsure of what to do with my top table. She is keen for my step-dad to be on the top table but I would rather have my brother with me but does that mean we would have to have my partner's sister included as well? I dont want to upset anyone but unless I can have 15 people up there I dont see how this can work?
It is really up to you who you seat the top table. I don't feel you should be constrained by outdated etiquette. The traditional seating plan of:
Chief Bridesmaid, Groom's father, Bride's mother, Groom, Bride, Bride's father, Groom's mother, Best Man
can be completely reworked to suit you without having to have 15 people at the top table (unless that's what you would like!) If you would rather not have your step-dad on the top table then you could simplify it for your needs to:
Chief Bridesmaid, Groom's father, Bride's mother, Groom, Bride, Best Man, Groom's mother.
You could either have a smaller scale top table without all the parents and step-parents:
Chief Bridesmaid, Groom, Best Man, with your parents at the table closest to the top table, or a sweetheart table for just you and your Groom, with your parents and bridal party at the next table.