I think by now they should know they can, it’s just a matter of setting up a safe way for them to contact us.
I haven’t really thought this through a lot, so we’d need to source ideas from the crowd. But roughly:
Owen, Dora, Kingsley and I pool our knowledge of the location of Azkaban and we make a plan to get people there. Get Unbridge to give us what she knows about where the muggleborns and political prisoners are. Formulate a plan. Get in, and portkey out with as many as possible. Use your resources to get them settled somewhere safe.