"Absolutely amazing, with no digging by the goblin herself, she manages to continue on as if nothing happened. LeShanna on the other end will have to try again if she wants to get through!"
"Whisper creates a maddening blend of colors that seem to only affect her own teammate Toxic, who drops to the floor as his eyes begin to swirl! We have a challenge here folks!"
Khan - Digging for the keys is an action.
Suggestion is one of those tricky spells lol it may have to go on the Survivor ban list due to the complications. However based on the line "It pursues the course of action you described to the best of its ability". Toxic will pull the lever as soon as he is given the opportunity (Whisper beginning the puzzle). However, it doesn't explicitly state the it makes the creature want the result to happen....so to that effect, I will say that Toxic can advocate for aid in ending the spell, but cannot attempt to end it his self, or not pull the lever while under the spell.
Now, because Toxic is now incapacitated by hypnotic pattern he obviously cannot pull the lever, unless he is knocked out of the trance. However, after consulting some Sage Advice, I do believe that suggestion continues to last on Toxic, due to it's duration of 8 hours, as long as Seth remains concentrated on it.
Seth smirked as Whisper tried to hit him and Anastasia with a spell but clearly it did not work. He was annoyed as Toxic was incapacitated though, thinking of something. 'Anastasia, hit him with a cantrip to wake him up when LeShanna gives the third set of keys to Whisper, that way Whisper won't be able to use any spells on him again and he'll be up just in time to pull the lever.' he then telepathically spoke to Anastasia so that no one would know, nodding his head at her. Seth was now preparing himself for any sort of retaliation.
Yes you would get advantage. Khan launches two arrows at LeShanna, however only the first one hits. - LeShanna you take 17 damage and please make a concentration check for Haste DC 10. If you fail, we can use your second action roll as your next action roll. If you succeed, then you have your turn as you previously described.
Toxic is correct, you only have advantage on your first attack. So your second attack is a natural 1, but it did miss anyways.