1) Does the effect increase by the number of models affected as what I understand "par chacun des combattants affectés" means?
That means that In cha'Allah is not gone an all warriors when You try to hit a single In cha'Allah affected warrior. But You have to try to hit every single In cha'Allah affected warrior in order to remove In cha'Allah effect from every warrior.
Ah, ok. I thought that part referred to "gagnent".
2) Does the effect last on if in the following attack sequence/s the opponent's model doesn't make an attack roll for whatever reason (because it has 0 CBT or for other game effects) what I understand "attaque subie" means?
Attaque subie is referred on any kind of attack Melee or Shoot.
You can try to get a hit with a Squamata War Disc and You will remove the In cha'Allah effect also if You did not hit.
You have to actually roll an attack die to remove In cha'Allah.
Yeah, that's what I thought. The warrior under the influence of In cha'Allah has to actually be the target of an attack roll and not just the participant of an attack sequence and that includes shots. Of course, one could say that "one sided attack sequence" isn't the same as "attack sequence" and "involved" can't mean units in contact lending assists, but I have seen people argue over less.