I'd have to recommend against this. Obviously, you want nothing best for your animal, but it can be tricky... It sound's like your one cat get's outside, and does fine, but if you have one that is terrified, she probably has never developed the skills to defend herself....
It's like if you put a ragdoll cat outside halfway through its life, and it runs into a raccoon, it has absolutely no idea how to respond, and isn't as fearful as a cat that's lived outside its entire life.
My cat Skittles is an indoor/outdoor cat, but she's been going out since she was a essentially a kitten, and is quite street smart (knock on wood)
Cheers!