In Aced's case I theorize that maybe he finally realized how close he was to truly "succumbing to Darkness" (i.e. similar to Luke in Return of the Jedi) and he had still enough dignity left to restrain himself there. Note also how when he speaks with Ira in the scene afterwards while he's still seething with rage at Gula's "betrayal" of keeping the Lost page from them (which I just realize was what I theorized from the get go, that Aced and Gula would work together first and then break apart when Aced learns about Gula having the Lost page, lol) and claiming he'd never forgive him for that, he doesn't articulate any further desire to eliminate Gula completely.
Later on though in Browser-Chi, at the confrontation with Ira at the fountain we get this exchange:
Ira:
| I came here because I sensed your bloodthirst.
|
Aced: | A final battle is no longer avoidable. |
| Invi, Gula, Ava, and you, too, Ira. All desperate to collect more Lux than the other Unions.
|
| The battle had already begun. It was you people who aggravated the situation. |
Ira: | Are you saying we must check them by force? |
Aced: | In the end, it's a strong leader who controls the world. |
| It's not Lux I'll gather more of than anyone—it's soldiers. |
| Strong organisation is imperative. When it comes to maintaining the balance, there need only be one leader.
|
| I'll banish the four of you, and unify all the Unions under me.
|
Ira: | Don't overestimate yourself, Aced. You aren't that strong.
|
| Let me show you how pride comes before a deadly fall. |
Aced: | I'll be waiting in the land of the final battle! |
By the end of Back Cover, the desperate collecting of Lux en masse (started by Gula first) has just begun, so Back Cover doesn't cover the entire scope of Browser-Chi, but here we can see that Aced's stance hardened even more by then and he's willing to "banish" all of the other four Foretellers, by now fully entrenched in extremist views which made many in the audience despise him back then.
In Ira's case there isn't really much to work with in regards to Ava, only that he was obviously displeased with her refusing to disclose Gula's whereabouts. Her mistaking his intentions however is also partly his own fault since when Ava inquires on what exactly he wants to do he only responds with "none of your concern", most certainly only fueling Ava's fears that he would somehow hurt Gula.
Otherwise there isn't much interaction between them at all sadly.
Invi certainly backpedals in their last conversation there because she realizes she's making the same errors as Ira, Aced and Gula already did, more or less successfully salvaging at least her relationship with Ava (for the moment). In this vein, Invi seems to be a little more perceptive, yet as already said her errors lie in a different field.
She also certainly tried to keep balance, but once Gula started to frantically collect Lux and Ira as well as Aced followed suit, them hoarding it for themselves instead of using it to protect the world, she realized things had already gone out of hand and are unsalvageable, that's why she tells Ava that they must "delay the inevitable" at the end of their conversation.
Gula certainly does understand her reluctance and probably deep inside already knows she's right too, but by that point I assume he was already sort of desperate, seeing the "summoning Kingdom Hearts and
possibly summoning back the Master"-plan as the only option still left, unwittingly causing things to get out of hand even further with starting to hoard Lux.
Being too passive is indeed Ava's main problem on the issue combined with her also being too reliant and dependent on the Master and his teachings.