If i have multiple Ivern Friend for all at a battlefield, have the requirements and successfully conquer/hold, do i score 3 points? (ex 2 ivern + conquer/hold)

Yes — with two Ivern, Friend to All meeting the tag condition, a single conquer/hold gives you 3 points: 1 for the conquer/hold itself plus 1 from each Ivern.

Each Ivern has its own separate triggered ability, so both trigger and resolve independently; the "once per battlefield per turn" limit (Rule 470) only restricts the Conquer/Hold Score itself, not points gained from triggered abilities. FAQ #10494 makes this explicit for the identical Ahri, Alluring wording: two copies on one battlefield plus the hold point = 3 points.

Two extra notes: each Ivern only scores if the condition is checked for it — so your units must collectively have all four tags (Bird, Cat, Dog, Poro), which two Iverns can help cover with their chosen tags. And points from Ivern's ability are not "Conquer" points, so they're not subject to the final-point restriction (Rule 471.1.a.1) — they can be the winning point even if your conquer that turn would only have drawn you a card.