There aren't too many prominent muggles to have them feature in this. The Dursleys maybe? Even they wouldn't really play a part in the Battle of Hogwarts though if Mariner is sticking to the storyline. Dumbledore is surprisingly alive though, so anything is possible.
Not surprised to see character claiming allowed. Tried to remember which characters might be in the 30, turns out there's about a million. Think we can probably rule out a Ministry side to this if it's just the battle. Not sure about dead characters seeing as Dumbledore has had an exception made for him - does that mean Sirius is alive too?
I reckon the Ministry may well be in this as a third party of some sort. At least I don't think we should rule out the possibility. Can't imagine what their win condition could be though so maybe just one or two characters maximum.