ok just to be sure, i recently played jon moore sammy vs sammy. now i understood sammies had priority on their effects as long as there was another sammy on the field already, for instance

A has irou on field

B has two back row

A summons yaichi and calls priority

B activates trap hole (example)

A yaichi still breaks other trap/spell (correct?)

but lets say it was vice versa

A had yaichi done first and then proceeds to summon irou

B activates trap hole

now my opponent calls chain link prority and breaks the other back row is this a legitimate move

if that is the other card you targeted with priority and you don't kill Irou to save Yaichi, I'm 99.9% positive you will still destroy the other card because there is another Six Samurai on the field of a different name.

You have the order wrong. When "The Six Samurai - Yaichi" is summoned when another Six Samurai monster is face-up on the field, the player who summoned Yaichi has priority to activate the effect to destroy one face-down Spell/Trap card on the field. The opponent then has the chance to respond after the target for Yaichi's effect has been chosen.

For example:

Player A has two face-down Spell/Trap cards on the field.

Player B has "The Six Samurai - Irou" face-up on his side of the field, and summons "The Six Samurai - Yaichi." Player B then uses his priority to activate Yaichi's effect to target one of the face-down Spell/Trap cards.

Player A now chooses whether to activate anything in response to Yaichi's effect.

When you declare you will be using priority for Yaichi's effect, you choose your target before your opponent decides whether or not to respond, not after.

To answer your other question, if a player has a face-up Yaichi and summons another Six Samurai, then that player does have priority to activate Yaichi's effect.

I hope this helps you.

Both are legit moves. Upon summoning its the TURN PLAYER that has priority, not the monster he summons. In either case you can retain priority to activate Yaichi, whether he was the monster being summoned or not.

When a player summons a monster (assuming nothing else has happened and they are in Main Phase without any other effects going on), the turn player maintains priority to activate a monsters Ignition effect or a Spell Speed 2 effect. Turn player may choose to not do anything of that sort and pass priority to his/her opponent to respond (not chain) to the summon. Its as simple as that. It doesn't matter if "Six Samurai - Irou" or "Six Samurai - Yaichi" was on the field first.