Walking down the isle

In your place, I'd probably stick with your mum. It sounds as if you are quite close to both your dad and step-dad, and asking one but not the other might hurt the one who isn't asked. And it's nice to shake up the patriarchal marriage stuff a bit sometimes by asking a woman to do a role that's traditionally always been given to a man!

I have a similar situation and my partner and i have decided to meet each other at the end of the isle and walk down together, this way there will be no upset on either side. Stick to you mum especially if she has been your constant xx