no reason why you couldn’t do this by using that same technique that you are using to loop through all the rows in the second table but on the first table as well.
however, if you are wanting to trigger this from the ‘check box’ event, can’t really see the point of wanting to then check all the other rows in the table. as the users then go to another row in your table to uncheck one of those checkboxes it only needs to be checking what they unchecked (ie current row) in your first table against all the rows in your other table.
the other option you have of course over all of this, is if you have your users ‘select’ by checking the checkbox in the first row, and then you present them with an option to ‘review selected items’, this being a button on your form, and the script under that is simply then going to hide the existing table and show them instead your ‘hidden table’ .. and then in your hidden table there is a column ‘remove’ that they can check and that simply does a ‘delete current row’, then things are a lot easier for you to manage as well.
you could even drive ALL of this from form buttons.. one button to say ‘add more users’ (that shows your first table and hides the second), another to say ‘remove users’ (that shows the second table and hides the first). as long as your notify action is set to the second table, it is only those email addresses that are then notified