I know that u can use outwit before posion in order to nullify the opponent defense so he takes the damage, but this apply to others free actions as well? For example, cyborg superman telekinesis + larfleeze summon an orange construct + outwit before posion?

All those free actions should be during the beginning of your turn. You could throw in a perplex or two in there as well, some free barrier with Arkillo, and you could still roll for leadership.

The beginning of the turn ends with the first non-free action (unless the action says that it can be given at the beginning of the turn). So you can use any and all free actiono at the beginning of your turn.

Poison: At the beginning of your turn, give this character a free action and deal 1 damage to each adjacent opposing character.

If there are multiples characters with poison, must they use it (consecutively), or I can give another character a free action between poisons?

Example: Opponent character has impervious and is based by 2 friendly characters, each with poison. A character outwitted his impervious, the first poison deal damage revealing invulnerability, a second character outwitted his invulnerability, then the second poison deal damage.

That sounds legit to me.