The mind that I do, what a sleep were this

For your advancement! Do you understand me?" (2.1.232-234)

Antonio asks Sebastian if he knows who is next in line if Ferdinand is most certainly dead and if Alonso were not alive. Sebastian answers that the next in line would be Claribel. Antonio rationalizes that Claribel is so far and further declares the waste of an opportunity that they are in. After all these implications and the statement above, Sebastian finally fully understands what Antonio is aiming for and says "Methinks I do" (2.1.235).

Antonio is like John Lennon below after Sebastian finally understands what Antonio has been implying.

ugur. https://beatlesdaily.com/2016/02/06/best-beatles-gifs-part-1-12-gifs/. 28 Oct 2018

What great hope have you! No hope that way is

Another way so high a hope that even

Ambition cannot pierce a wink beyond." (2.1.205-208)

Pushing the idea that this moment is so convenient and shaking his head at the shame it would be if Sebastian did not carpe diem, Antonio does not directly instruct Sebastian to kill Alonso. He does numerous things with his rhetoric. First, he gives Sebastian the idea that he formulated the plot to murder hiimself. Second, Antonio numbs Sebastian's conscience. Thirdly, Antonio is able to effectively paint a glorious image of all that Sebastian can achieve.

Antonio essentially gives a knowing nudge to Antonio with a "What happens in Vegas, stays in Vegas" feeling, which would muffle Sebastian's conscience.
Quite like John Mulaney with his mischievous eyebrow-raising, Antonio acts very roundabout and suggestive. Antonio and Sebastian would be in on a very big lie if they killed Gonzalo and Alonso.

Gifer. https://gifer.com/en/6wba. Accessed 27 Oct 2018.

Who hath cause to wet the grief on ’t" (2.1.101-102). Sebastian says that at least Alonso's daughter is not here to remind Alonso of what he has lost in his journey. Sebastian does not seek to uplift Alonso's spirits like Gonzalo, but instead wants to blame Alonso and make insensitive, biting comments.
Comically, one can say Sebastian is like the depicted doctor with his lack of empathy and touch of belittling comedy in this tragic shipwreck. The mood of the scene is comical itself despite Alonso's sadness because of the funny comments by Sebastian and Antonio.

The New Yorker. https://www.newyorker.com/cartoons. Accessed 27 Oct 2018.

Execute all things. For no kind of traffic

Would I admit. No name of magistrate.

Letters should not be known. Riches, poverty,

And use of service—none. Contract, succession,

Bourn, bound of land, tilth, vineyard—none." (2.1.123-128)

Gonzalo speaks of a utopia he imagines he could create on this island. As there is a strong theme of hegemony throughout the play, with jokers like Stephano and Trinculo incapable to claiming authority, and a magical, imperialist like Prospero easily grasping and maintaining power, Gonzalo has a rare moment highlighting his own desire for power, albeit not with a very egotistic light. Shakespeare portrays Gonzalo as a kindly man with intentions "To feed my innocent people" if he were the ruler of such a land (2.1.239). Shakespeare appears to put forth the idea that people with some level of kindness or mercy, like with Prospero's decision to not seek vengeance on Antonio and set Ariel free, are wise people to give power to.

Strangely enough, Gonzalo's rambling about this ideal state seems to set up a serious, thought-provoking moment for the audience, despite Antonio and Sebastian's jests. Gonzalo's dream is quite like John Lennon's in his song "Imagine," where he asks people to imagine a world with no wars, materialism, or nations. It was easy for critics to laugh at Lennon's song for its idealism, like Sebastian and Antonio laughing at Gonzalo's ideal world, but their dreams are nonetheless intriguing.

Giphy. http://gph.is/2clzv5Z. Accessed 27 Oct 2018