How to get Ultima?

[BG-57]

That's true.

As for Zodiac, you could theoretically have up to five units learn it directly from Elidibs. It might make things easier if you have somebody other than Ramza pick it up, because Elidibs prefers to target other units than Ramza with it. Ramza was only able to learn it because I waited for him to start casting on someone else then moved Ramza into the area effect before he finished casting.

Zodiac can only be learned by Summoners that are hit with it and survive or by picking up a life crystal from a Summoner that knows it. So either way, you're going to have to teach enemy Summoners Zodiac to get everyone in your party to learn it (since you can't hit your allies with attack Summons).