Depression is a real bitch. It manifests itself differently in everyone. Perhaps coaxing someone to see a therapist, go out or whatever would actually help them. But that's not going to be true for everyone and the coaxing may do more damage than good if it's unprompted. If they express interest in anything (e:g; going to a movie, seeing a therapist, going to the gym), that can be a good time to give them a small nudge. I hope your friends find some light in their tunnels.

Interestingly, it's often exactly the opposite that's needed: just be there and listen.

Once that bond has been made, then one can start to work on improving things.

All of this requires time and a lot of energy.

Verbally expressing your love and support for your friend, and helping them see the positive aspects of their self, their situation, and the world around them can go a long way. If you can get them to talk about their views, and help them see when they're stuck in unproductive negative self-talk, that can be truly eye opening. Help them love themselves. Encourage them to come on a walk or run or other exercise with you; don't force them or over pressure them, but say that you promise they'll feel better.