It is your choice whether to let your cats outdoors once they are spayed/neutered..the problem with your current situation...you are allowing an intact female and her intact kittens outdoors with other intact cats. Not only would I be concerned about the potential for her to be pregnant again..but every time she is mated by an intact male, there is a chance that that male is carrying a disease such as FIV or FELV that could be transmitted to your cat and/or her kittens. I guess my question is...is her freedom worth her life???Also it's a very common practice in this country to have your cats free to go out - infact all the cats I've seen till date are usually outside the house all day and no friend has ever had a cat killed by a dog - tho I've heard of very young kittens getting run over by cars - also maybe because she's a cross between a stray and a persian cat she's a bit stronger and streetsmart by inheritance I think.
I do intend having her go out and the kittens once they'r old enough to take care of themselves, but I'll wait for time to help me make a firm decision on that. But seriously it's a regular norm here for cats to roam around, come back to feed, sleep, etc, but be cats generally - infact my cat's the first one i've seen whose truly been a total housecat since I didn't have a choice.
After your cat has been spayed...the chances of males trying to mate with her goes down significantly...so does her chances for diseases, pyometra and certain cancers.
Another misconception that is out there is that cats must be in heat to become pregnant....an intact cat can become pregnant at any time, by any intact male. She can also become pregnant again within days of giving birth and that is something that is not recommended.
Her kittens could become pregnant as early as 4 months of age...so my advice is to find a vet who is willing to spay/neuter all the kittens as early as possible. Definately get mom fixed now...she can still nurse her kittens.
Katie