Hi, Welcome to Groovy
I had 2.5 sets of parents, which was slighty easier to deal with!! I decided on a top table as I was able to space them out
I only had my mum and brother, but Mark has the 2 sets, so I did it like this (imagine you are a guest looking at the table!)
Step-dad, Mum, Best Man, My Mum, Mark, Me, Brother, Chief Bridesmaid, Dad, Step Mum
I'm thinking maybe you could have 12 on the top table, as 10 didn't look too odd at our wedding, how about (again, looking on):
H2b's SD, H2b's Mum, Best Man, Your SD, Your Mum, Groom, You, Your Dad, Your SM, CBM, H2b's Dad, H2b's step mum
I personally found it easier to have them all on the one table facing out so they couldn't mis-behave (not that they would've, but I didn't want any bitchin' on my day!!!)
Hope this helps, tell them this is only for 2.5 hours and would mean so much to you and H2b
So, anymore details? Share with us please, we're a nosey bunch
Lo xx