How can I unstick lollies stuck in a jar, welded by heat?
You could try freezing them, if you want to remove them from the jar cleanly. However, it's possible all humbugs will stick together.

You could also try heating it (microwave shortly, or put it in the sun again), and remove bits while they are still warm. I would put the jar afterwards in the dishwasher to remove residuals.

However, I'm afraid both methods won't be able to have the individual humbugs out.