For Ivern - Friend to All's bonus point, do the Bird, Cat, Dog, and Poro units all have to be at the same battlefield?

No, the Bird, Cat, Dog, and Poro units do not have to be at the same battlefield to trigger the ability on Ivern, Friend to All.

The card text specifies: "When I conquer or hold, score 1 point if your units have all of the following tags among them — Bird, Cat, Dog, and Poro."

Because the condition specifies "among them" rather than "at this battlefield" or "at the same location," the ability checks your units across all locations you control (including your base and all battlefields). As long as you have at least one Bird, one Cat, one Dog, and one Poro currently in play under your control, the condition is met.