Unfortunately, insomnia is often caused by worrying, so as your husband is suffering from depression and anxiety and being treated for it, it is no help knowing that dealing with the worries or anxieties might help.
I know this scenario very well, as my husband only sleeps five hours or so out of every 24.
I suggest you think about when in the course of the day you eat your meals, and how often your husband eats and what he eats.
Sometimes it is easier to fall asleep if a main meal is not eaten late in the evening, or even in the evening at all. Some find that coffee or tea drunk in the evening makes insomnia worse, and that a hot milky drink helps sleep.
However, if your husband is anything like mine, he will neither give up drinking coffee all round the clock or swallow anything hot and milky!
What does your husband do all day`? Mine tends to sit on the sofa feeling sorry for himself, and watching TV series that certainly don't stimulate his brain!
On the days when I can get him to take a bike ride, do something or other in his workshop and preferably finish the task as well, he does sleep better.
Likewise, only watching the News during the day, as opposed to just before bedtime helps too.