Kia saunters over to the zombie poking the painting with the dead girl’s foot and bodily pushes the zombie into the painting. Let’s see if animated dead things trigger it. 

Nothing happens.

"Dispel Magic time?"

"It's almost like the picture will only swap with a being that's alive.." Ezmerelda ponders.

OOC: I volunteer one of the NPCs!

(You volunteer as tribute! *shoves Ezmerelda*)

Bors teleports out of the painting with, surprisingly, all of his previous gear, slightly startled. The painting has changed to a horrified, chained, naked Ezmerelda - and remains motionless.

Stella puts up her fists and takes a step back. "What have you DONE?!"

Briella grabs Grishkar by the neck and pulls him in close. Briarfang growls at the skeletons warning them to stay back.

"What in the Nine Hells do you think you are doing, Necromancer." She snarls.

She keeps hold of her holy symbol the moment Briarfang give a warning or Grishkar makes some kind of attack she's Turning Undead.

“Briella, wait. What if you placed one of your animals in the painting and then dispelled them? Is that something that that you could do?”

"My bag doesn't work like that. The animals stay til dawn and then disappear. I don't know if the painting's magic will cancel that out or not."

Briella sighs and looks at the painting.

"The best thing I can do, short of shoving Grishkar, in is trying to dispel the magic that holds her in the painting."

"I don't know if this is a trap that I have the skills to disable.  My sense is that it's of magical origins, and hence, could be defeated by magical means (Dispel Magic)."

OOC: In 5e, how the heck does a rogue disable a magic trap?  Is it a DEX based check with thieves tools, or an Intelligence (Arcana) check (not using thieves tools)?

Grishkar extends a hand to his minions to keep them still, "I took the initiative where no one else would. Tell me," Grishkar's gaze probes into Briella's looking to weed out the weakness of Good, "Would you have done the same to sacrifice anyone but me? Would you leave Bors to eternal imprisonment? Would you have gone in yourself? You call me evil because I make the hard, pragmatic decisions. I am a servant of a higher power, just as you are, but mine is a path of finality and survival. You don't get to where I am or come out of what I have been through by being gentle."

Grishkar's wand delicately slides out of his sleeve and flicks to Briella's hip. The dire wolf braces with a snarl, "Make a move and make it count, priestess, because if I don't kill you, then you may as well be tribute for the painting because Strahd won't be beaten by half an elf."

You all get a sense that this painting is not something of this world. Or beyond.

By the way i'm loving this exchange.

Martha levels the sword towards Grishkar, “You know for someone claiming pragmatism and logical thinking, it doesn’t seem like it. If you asked me, it seems like impulse. You didn’t take time to observe the abilities or weakness of the painting, only thinking in the short term. We don’t know where to go now, do we? You wanted Bors immediately, and even now you threaten the wielder of one of our artifacts. No offense, but you’re not nearly the cleric that Briella is, and I doubt the symbol would care for you much. In fact... of all of us, you’re the most expendable. The pragmatic thing is to eliminate the person who will clearly betray us. But of course, I’m a big practitioner of grace and second chances. What’s it gonna be?”

"Guys, KNOCK IT OFF.  Quit fighting amongst yourselves.  You have NO IDEA how strong Strahd is, and if we have ANY chance of lasting longer than 6 seconds with him, we need to ALL work together.  Put aside your animosities, and focus them on our task at hand here.  Now.  What can WE as a GROUP do to get Ezmerelda out from that painting, so we can make ourselves whole again?  Only as a GROUP can we see any chance of surviving our fight with Strahd."

"Martha watch him. Grishkar if I can't get her out you better pray that your god strikes you dead were you stand, because I can only imagine how hellish its going to be for you to be trapped in that painting with no way to perish." She releases the necromancer but turn to Briarfang.

"Keep him in line."

She walks over to the painting and cast dispel magic.

Nothing happens. You hear a very low growl, so low you barely hear it - as if the very walls of this lower level were shifting. Changing. The hallway you just came down from before the painting seems a bit more distant now. It is nothing but more rooms and darkness ahead. 

I grab Grishkar and throw him into the painting, Briarfang helps.

Martha stops Briella, “Wait a minute. Let’s not do anything too hasty here. There’s got to be a way to do this without throwing more people into this stupid painting.”

Oh shit, this group LOL. LOVE IT.