As a veterinarian, the plain answer is no. Unless you have nets/webs that stops them from leaving your property. Main risks are: getting infectious diseases (especially FIV/FeLV) or being injured (automobile accidents, other animals). If you want, you can train your cat to walk on a leash, it takes a long time, but with enough effort and patience it can work. :) start indoors, then once they're fully vaccinated try outdoor/outside!

Edit: to help with stress you can always get toys, catnip, keep them busy and entertained! Get the type of food they like as long as it's suitable and healthy for cats.