Lifelink, counters and death

[Oldschoolmtgnoob]

i attack with a 3/3 creature, opponent blocks with {ajani's pridemate} and {child of the night}.
Now which comes first? The lifelink giving giving counters, saving one creature? Or do all die?

[Spikepit]

Lifelink still gains you the one though, right? While Pridemate's doesn't as it's no longer there when it checks? That's how DotP2015 makes it seem to me...

[Kaylesh]

Sequence as follows: creatures block, deal dam, lifelink says you gain life. Then Ajani's ability triggers. Yet Ajani and vampire got lethal dam so go to gy. Ajani has left the field when his ability resolves so the counter goes nowhere.

I will edit in the rulings.
119.3f: Damage dealt by a source with lifelink causes that source's controller to gain that much life, in addition to the damage's other results.

704.5g: If a creature has toughness greater than 0, and the total damage marked on it is greater than or equal to its toughness, that creature has been dealt lethal damage and is destroyed. Regeneration can replace this event.

112.3c: Triggered abilities have a trigger condition and an effect. They are written as "[Trigger condition], [effect]," and include (and usually begin with) the word "when," "whenever," or "at." Whenever the trigger event occurs, the ability is put on the stack the next time a player would receive priority and stays there until it's countered, it resolves, or it otherwise leaves the stack. See rule 603, "Handling Triggered Abilities."