Be VERY careful. My father-in-law told me about his old budgie. The cat never pounced or even tried for YEARS. He'd just look at the bird doing his thing. Then one day out of nowhere the cat pounced and killed the bird instantly. So never let your birds out.

If you want to get them to know each other just do it ALWAYS with the birds in the cage (mostly in hopes to prevent a curious cat harassing the birds at night).

I have no screens on my windows and when it was still hot I had my birds in their cage by the window with their door pointed towards me. They enjoyed themselves until a cat pawed curiously at the cage. Poor birds were scared to death. I yelled at the poor cat who was only being curious...poor birds and kitty. Though that same cat later wandered into our house and started acting like he owned the place