$count = count($objects);

$id1 = rand(0,$count);
$id2 = rand(0,$count);
$id3 = rand(0,$count);

function get_rands($min, $max, $amount)
{
    $rands = array();
    $rand = false;
    
    for($i = 0; $i < $amount; $i++)
    {
        while(!$rand || in_array($rand, $rands))
        {
            $rand = rand($min, $max);
        }
        
        $rands[] = $rand;
    }
    
    return $rands;
}

// Usage
print_r(get_rands(1, 5, 5));