My father asked that my stepmother be escorted to her seat. I know that it is my decision as the bride rather than his, but I'm ok with his request since my mother passed away several years ago. I'm trying to think about the seating prior to the rehearsal - is this okay?
1. 1st row left side - Seating of my paternal grandmother (groom's paternal GM will not be there for the wedding, both maternal GMs and maternal/paternal GFs are deceased)
2. 1st row left - Seating of my stepmother
3. 1st row right side - Seating of groom's mother - usually she would be second, but I am actually closer to his mom than my stepmother.
I don't think my grandmother would want to be in a row by herself. Stepmom will also have a corsage along with grandmother.
Normally, if you were seating your stepmother as your mother, she would be seated last. But, it appears that you don't want it to appear as such, which is fine.
You have a very good grasp of how this is done. It is fine the way you have it now.