Bash commands inside vi

You have to turn on extglob:

#!/bin/bash
shopt -s extglob
cat ~/my/+(a|b)/doc

+() is an extended pattern, is only recognized when extglob is enabled. By default extglob is on in interactive shells and off in non-interactive shells.

If you type

command 1 & command 2

this is equal to

command 1 &
command 2

i.e. this will run the first command in background and then runs the second command in foreground. Especially this means, that your echo "done" is printed after command 2 finished even if command 1 is still running.

You probably want

command 1 &
command 2 &
wait
echo "done"

This will run both commands in background and wait for both to complete.

If you press CTRL-C this will only send the SIGINT signal to the foreground process, i.e. command 2 in your version or wait in my version.

I would suggest setting a trap like this:

#!/bin/bash

trap killgroup SIGINT

killgroup(){
  echo killing...
  kill 0
}

loop(){
  echo $1
  sleep $1
  loop $1
}

loop 1 &
loop 2 &
wait

With the trap the SIGINT signal produced by CTRL-C is trapped and replaced by the killgroup function, which kills all those processes.