Can we pass argument to a form from a Twig template
I think the most elegant way is to modify your controller so all the logic happens in the controller and only the markup in twig. If you have that option that's the way to go.

That being said, there are ways to get what you want.
The most convenient way I know is the twig_tweak module and use the function 

{{ drupal_form('yourmodule\\namespace\\Form\\yourForm', sourceid) }}


I have not tested it myself but it should work.