If I have a void hatchling on the board and play double trouble or ivern which say: look at the top 3 cards you may reveal a unit... Does the void hatching trigger at all?

Short answer: Void Hatchling doesn't "trigger" at all — it's a replacement effect, not a triggered ability — and it hooks onto the reveal part of Double Trouble / Ivern, Nurturer, not the "look at the top 3."

The look-at-3 is a look, not a reveal, so Hatchling has nothing to apply to there — same reasoning as Stacked Deck (FAQ #1404). But both of those cards then instruct you to reveal a unit from your deck, and that's the instruction Hatchling replaces: you look at the top card of your deck first (which will be one of the three you're already looking at), you may recycle it, and then you reveal a unit from among the looked-at cards and draw it.

Practically, that's a small upgrade — you get to bottom the top card before making your choice instead of having it swept up in "recycle the rest" afterward — and note if you recycle the card that was your unit, it's gone before the reveal happens.

One caveat: FAQ #766/#1404 establish the look-vs-reveal split and that Hatchling replaces rather than triggers, but I didn't find a published Q&A that runs it against Double Trouble/Ivern specifically; the above is the Rek'Sai precedent (FAQ #315) applied to these cards.