1. The mark appears to be an ordinary tattoo, though if it is, it isn't behaving like one as it's already fully healed.
2. The kitchen does not replenish while they are trapped within.
3. There is nothing more to find under those particular loose boards.
4. Just ash.
5. BECAUSE REASONS. Shouldn't have stolen a lantern, Elena, you could have been partying at the Mystery Mansion instead.