Seating

Does your mom and dad having siblings? They can sit with them? Same with your FH's parents.

If not - maybe they can just sit with other family members? Mom with mom's side of the family, dad with dad's side of them family.

I'd just seat each of them with their family members (or friends), i.e. your dad with his family, your mom with her family, etc. You could ask your siblings which parent they'd prefer sitting with, or just assign them to whichever table you think they'd prefer. You definitely don't need to seat all of the parents at one table!

We have this problem with FH's parents too, they are divorced and do not speak. We are just seating them each at their own tables with associated family (siblings, grandparents etc). No "parents" table. My parents have their own table with my sister and other family. I would just avoid parent/vp tables like you mentioned and group people with whoever they get along with best. I'm not sure what to do if noone wants to sit with your mom at all, but I guess just pick whoever is the least likely to cause drama over it.

Yes, that's okay! No one will know the difference/pay attention to who is sitting where.

Put them all at separate tables and seat them with their own family members or with other guests. You do not need specific "VIP" or "Family" tables at your wedding. As long as your guest match up isn't super awkward (I tried to put together people who already knew each other or had something in common together) it will be fine.

I'm not doing a parents table. I'm having my dad and step mom sit with his brother, and their family and my sister/BIL. I'm having my mom sit with her parents and her brother & his family. My FH's parents are still together, so they'll sit with FMIL's parents, and his siblings & their SOs