So, to keep this short, Venom is trapped by the ice and you two are both outside the stomach/in the original field.
The scenario that happens is that the Fire would be sent out, burning the toad stomach (while also overcoming the ice that 'protects' it), and clash with the water, producing steam which by both of your acknowledgements would cover the entire field/container. For future reference, by damaging the toad stomach, you would be 'reverse-reverse summoned' back into the original field. Anyways, the main point is that the clash between the fire and water (which continues even after the initial clash that damages the toad; due to them being streamed techniques) would produce steam in large quantities, that, once again, you both acknowledge to be plentiful and spread out. Z then freezes over the mist, except around herself.
Now, there are a few issues in the fight, though they happened before and were not addressed, so I'll skip over them, but the location is one that is still relevant. Venom says he moves away from his original path, but does not say that he moves away from the mist, so he will still be captured. As for Z, while not encased by the ice, she is somewhat 'trapped'. She freezes all the mist, except around herself without specifying to what extent. So, going with what was said "Pushing her staff forward, another glyph activated, creating an ice block in the entire room, save for around Jaina" would result in an ice block that covers the area the mist was in, except a small portion where Z is in. Given that you guys didn't specify where it reaches and Z wasn't specific in describing to what extent around her, we'll go with Venom being frozen, and Z being in a gap/safe area inside the ice.
If you guys can work out specific locations and dimensions with eachother then great, if not I suggest that Z is in a safe space of 1 meter radius inside the ice, while Venom is trapped 7-8 ish meters away. Let's say the ice itself covers 15 meter in each direction, so you both have ice reaching a meter or so behind you, although on Z's side it's slightly less durable since there's a gap. Oh, and on the note of Z describing the area as if it was inside the stomach, it doesn't matter that much since her intention of freezing the mist works regardless. You guys should try to be more specific though to avoid stuff like this.