Major depressive disorder can also be a serious disease that a lot of people don't fully understand....
It isn't always because someone just isn't in their natural habitat, or they play too much video games. It can be a seriously debilitating disease that makes a person chronically exhausted, perpetually in a poor mood, cognitive problems, memory issues, depression headaches and physiological pain, etc. Some depressed people will literally just sit in bed crying all day, and have no real reason why. They can't do anything else because they don't have the energy to do so. They can't simply think happy thoughts or go to therapy and talk about their feelings and expect the depression to be resolved.
Depression is just a collection of symptoms though....There are a lot of underlying issues and things that could cause depression, including underlying medical issues. It isn't always just because someone experienced psychological trauma.
There are a lot of things that are correlated with being helpful for those with depression depending on what the underlying cause of the depression is. Some things can be more helpful than other things based on the individual. A few things off the top of my head.
-Talk therapy
-Therapy lights / lamps
-Cardiovascular exercise (including something as simple as slowly walking outside).
-Eating a whole foods anti-inflammatory diet (Look up MIND diet)
-Limiting sugar / sugary drinks / and processed foods.
-Positive IRL social connections (which is especially challenging for someone with depression)
-Fish oil
-St johns wort
-Creatine
-L-tryptofan (Although the scientific data here is not very strong)
-A good multivitamin (especially one that has a lot of B vitamins)
-Having consistent wake up and bed times, and good sleep hygiene(Sleeping in a cool but not too cold, dark, quiet room)
-Getting outside during the day and having sunlight on the retina - specifically shortly after the sun comes up and before sunset. The mechanism is similar to the therapy lamps
-Preparing for bedtime (Specifically not eating or drinking anything but water several hours before bedtime, not exercising before bedtime, not engaging in anything stressful several hours before bedtime, and not staring at computer screens).
Cortisol and melatonin compete with each other in the brain, so too much stress before bedtime can make it harder to sleep. Similarly having a lower body temperature is another indicator the body looks to to help sleep, so exercising before bedtime is a horrible idea.
-And of course the normal antidepressants are a miracle for some people.
*Hugs*
Best of luck. Maybe if the older two are not depressed they will be more motivated to work. :)