So long as they are kept frozen, they won't "spoil" in the sense of decomposition. The bacteria and enzymes will either be dead or inhibited. When we talk about food "spoiling" in the freezer, we are usually talking about damage in the texture and taste of the food which makes it unpleasant to eat, but doesn't mean you'll get sick doing so.
The issus with keeping any food for long periods of time in the freezer is oxidation and dehydration, freezer burn, both or which are caused by exposure to air. Oxidation is less of an issue here (talking about whole animals not steaks), but things in the freezer will slowly lose moisture to the surrounding air.
To prevent dehydration, and the food from becoming the worst kind of meat jerky, keep food in SEALED packages with LITTLE AIR (either pushed out, or vacuum sealed if you're fancy) and REDUCE EXPOSURE to new air (don't open and reseal it a bunch of times).