Declaring a var, placing it in a query and using the output of the query?

First, this is confusing:

$result   = $newdb->get_results("SELECT ".$column1.",".$column2."  FROM members");  
$columnq  = $newdb->get_results("SELECT ".$column1." FROM members");
$columnq2 = $newdb->get_results("SELECT ".$column2." FROM members");

You should only need the first of those or the last two (with one alteration).

Secondly, get_results will return an array or an object (default), so using it as you do here isn’t going to work:

'post_title'   => $columnq,

post_title does not accept an array or an object as a value.

If you want to retrieve a single string value from the database use get_var. Then this will work:

$columnq  = $newdb->get_row("SELECT ".$column1." FROM members");
$postargs = array(
        'post_title'   => $columnq,
        'post_status'  => 'draft',
        'post_type'    => 'bedrijf'
);

To retrieve a single row use get_row and with proper syntax:

$result   = $newdb->get_results("SELECT ".$column1.",".$column2."  FROM members");  
$postargs = array(
        'post_title'   => $result[$column1],
        'post_status'  => 'draft',
        'post_type'    => 'bedrijf'
);

But your code is still a bit confusing as you appear to be retrieving all rows from your external database/table but trying to use those rows as if they were a single row.

$columnq  = $newdb->get_results("SELECT {$column1},{$column2} FROM members");
foreach ($columnq as $c) {
  $postargs = array(
      'post_title'   => $c->column1,
      'post_status'  => 'draft',
      'post_type'    => 'bedrijf'
  );
  // code to insert post
}