Some risks of keeping your bunnies outside are:
1.) Harsh Weather Conditions- Even if extreme weather conditions like blizzards, hurricanes, earthquakes, or tornadoes don't happen often where you live, even cold or rain can be harmful, as rabbits have a hard time regulating their body temperatures on their own.
2.) Predators-- Rabbits can die of fright, so even if the cage is very secure, and no animals can get in, if one tries to attack your rabbit, he/she may die from fear.
3.) Bugs- Rabbits can get fleas and parasites, just like cats and dogs!
4.) Loneliness- While you may try to give your bunnies as much love and affection possible, you will be able to provide much more love and affection if your bunnies live indoors! My bun free-roams my room, and we always cuddle at night.
Of course, your bunnies may still thrive outside! Just keep those things in mind beforehand!
Good luck!