No. Because the Opponent is carrying a shield, she is by definition Unpinnable.
Yes, but not really. Player Characters and Companions are considered to always succeed in their check versus the DL if they are unwilling. If the Player playing the Player Character or controlling the Companion doesn’t want to be the Target of the Switch Places Magic Spell, it doesn’t have any effect.
Yes. Areas that are part of a Flooding only prevents spells that cause Burning Fires to take effect (such as Greek Fire or Trail of Fire).
All Opponents have access to the Unarmed skill. See the rulebook pages 21 and 22, under the heading Brawls. Companions and Opponents use their Attack Value but attack using Unarmed instead of their regular weapon. The damage is 1 + ES.
No. Retinue cards that are in the Party remain at their Experience level even after the Opponent and Retinue Level is raised. They remain with the Party until they are dismissed from the party.
Yes, all summoned creatures remain in the Battle until they loose all their Hitpoints or until the end of the last round of the duration for the Magic Spell.