When selecting multiple nicks, you can return the list using $snicks
This returns a comma separated list, which means the entire list is part of $1
To see if more than one nick was selected, use $snick(#channel,N) where N is the number of the selected nick.
eg: $snick(#channel,1) returns the first nick selected
$snick(#channel,4) returns the fourth nick selected (or $null if there isn't a fourth selected nick)

$2 would not be filled until a space character was encountered.

Code:
menu nicklist {
  $iif($snick($chan,2),$style(2)) EWhois: whois $1 $1
}