[I'm New] How Does "Sucker punch" work in VGC?

Correct me if I am wrong, Basically in a 1v1. Suckerpunch will work if the target uses an attacking move. If they use a priority move, it will only work if the sucker punch user is faster.

Bascially if Kingambit tries to sucker punch an aqua jet basci, it will always fail cuz basci is faster? is this correct.

In VGC, This is where I am confused.

I just played a game where they had Basci and Kingambit. I had lopunny and Ceruledge. I closecombat the kingambit and shadowsneak the basci and the opponent's sucker punch failed. Shouldn't it not fail cuz the loppuny targeted Kingambit with nonpriority move?

Also, If I am facing 2 targets. I sucker punch a target that chose a status move and the other target uses an attacking move on me. Would my sucker punch fail?