why would you try something like this,

create a variable array that contain all the Hollidays

    $currentyear=the current year;
    $holiday['01-01-'.$currentyear,other holiday,other holiday];
    
    $result=$start_date->difference($end_date, 'days');
    for(ctr=0;ctr=sizeof(holiday);ctr++;)
    {
    	if(holiday[ctr]>=start_date && holiday[ctr]<=end_date)
    	temp++;
    
    } 
    $result -= temp;