What do you mean by “both banners”?
Targeting the site is the point, right? Yes, it’s compulsory. That’s 1 defence die. Targeting the usurper must add 2 more, optionally targeting the pawn adds 2 more, and merely allows you to move the pawn since he has no favor to burn. The mountain subtracts 1 attack die. GeeBizzle has the option to use horse archers, which will subtract another 3 attack dice.
Neither banner can be targeted, so I have ignored that line for now.
Does that all line up with your intent?
5 defence dice and 4 warbands vs. 8 (or 5) attack dice and 9 Warbands. Looks optimistic to me. I’d say about 1 in 4 chance of success, assuming GeeBizzle uses the horse archers and you are willing to sacrifice all your Warbands.
You can choose to use less than all of your Warbands.