Killing everything except for a certain player in a certain radius

Solution 1:

If you'd like to be excluded from a global selector, simply use a scoreboard to exempt yourselves.
This is due to the way entity selectors work, which does not allow you to specify specific players.

/scoreboard objectives add noKill dummy noKill

Now, tag yourselves for not killing, and run this in a 20Hz redstone clock, in the order it is provided:

/scoreboard players set @e noKill 0
/scoreboard players set [Your username] noKill 1
     <Repeat for as many players>
/kill @e[score_noKill=0,score_noKill_min=0,r=100]

This way, you're marking everybody to be killed, exempting yourselves (by not making your score 0 and setting it 0 or nothing) then killing those who hasn't been exempted yet.

You can add more to the exemption list by adding a block with the following command before the last and after the first command blocks:

/scoreboard players set <Selectors and modifiers> noKill 1

Note: I may have gotten the syntax a bit wrong.

Solution 2:

/kill {radius 20, type=!bob8898, type=!coach0512} is very close, but this is how you do it:

/kill @e[r=20, type=!Player]

This will kill everything but players.

To do this if you are on a server with more than 2 people, we will use teams. this is a slightly easier way to do it than using scoreboard variables.

/scoreboard teams add noTeleport noTeleport

/scoreboard teams join noTeleport bob8898 coach0512

/kill @e[r=20, team=!noTeleport]

Solution 3:

/kill @e[type=!Player,r=1000] should work