Anyway, when i attack with ibex all my creatures will get +12/+12 (that part is fine) my question is, will the two new Ibexes (Created form Blade of selves) also boost my army? (In other words, will my creatures get and additional +24/+24? Or is the fact that they come in already attacking not trigger their effect?)
Unrelated question: Cards with Channel (Like Shinen of Life's roar) can you use the channel ability at instant speed?
An ability that triggers "whenever [this creature] attacks" won't trigger if a creature with that ability enters the battlefield attacking; for the purposes of that ability, "it never 'attacked'" this way (C.R. 508.4; see also this thread). Thus, if a token that's a copy of Pathbreaker Ibex enters the battlefield attacking, that token's ability won't trigger.
In general, a player can activate an activated ability (including one with a cost of the form "[cost], Discard [this card]") any time they have priority, unless the ability specifies otherwise (e.g., the ability says "Activate only as a sorcery" — compare Shinen of Life's Roar with Ghost-Lit Stalker [C.R. 307.5]) (C.R. 117.1b; see also this thread). Note that the channel ability word, like all ability words, has no game mechanics inherent to it (C.R. 207.2c).
EDIT (Apr. 20, 2021): Edited to conform to rule changes with Strixhaven.
Anyway, when i attack with ibex all my creatures will get +12/+12 (that part is fine) my question is, will the two new Ibexes (Created form Blade of selves) also boost my army? (In other words, will my creatures get and additional +24/+24? Or is the fact that they come in already attacking not trigger their effect?)
Unrelated question: Cards with Channel (Like Shinen of Life's roar) can you use the channel ability at instant speed?
In general, a player can activate an activated ability (including one with a cost of the form "[cost], Discard [this card]") any time they have priority, unless the ability specifies otherwise (e.g., the ability says "Activate only as a sorcery" — compare Shinen of Life's Roar with Ghost-Lit Stalker [C.R. 307.5]) (C.R. 117.1b; see also this thread). Note that the channel ability word, like all ability words, has no game mechanics inherent to it (C.R. 207.2c).
EDIT (Apr. 20, 2021): Edited to conform to rule changes with Strixhaven.