Here's what I would do. Buy some certan:http://www.beeworks.com/usacatalog/items/item134.htm
Spray all the combs that don't have bees on them and put them in storage. You can even spray the combs with the bees on them with certan if you think they are really infested with moths. Take the combs that do have bees on them and put them in the smallest box you have that that many frames will fit in. In other words reduce the real estate that the bees have to take care of. Look for other reasons they may be failing. Does the brood look healthy? Are there sunken cappings? Are there bees with deformed wings?
Moths don't kill hives, they take advantage of weak hives. You need to find the root cause of the problem of why the hive is weak. Likely suspects would be brood diseases mites, viruses, failing queen, etc.