New kittens??!!

I adopted a feral cat who gave birth to four kittens, ( one died a week after even though I was giving it everything I had). Anyway, I have three other cats and I was wondering how I should introduce them to them. I'm keeping the mom and kittnes in an upstairs closet and
I've brought the kittens out a couple times and showed them to my three other cats and they're curious at first, but after they smell them they growl and hiss. I was wondering if anybody out there has had any expieriance or knows what to do. At what time should I try to bring them out into the open? Also, how soon can they eat solid food?
Thank You,
Stefani

Please keep the kittens with the mom cat and away from the other cats until they venture out with mom on their own. You don't say how old they are, but they should stay secluded with mom until she decides it is time to explore. As the kittens get bigger, they will start to follow mom around and start eating out of her dish. For right now, feed mom good quality food in small amounts about 5-6 times a day. Even giving her kitten food (dry) will help her to keep up the strength she needs to nurse these kittens. But if you keep introducing them to the other cats and keep taking them away from mom, you stand the very real risk of mom suddenly rejecting her own kittens (because of smells on them)

I am also moving this to the feral forum for you.