How old are they? And who on earth gave you pedigreed unaltered kittens? That's VERY uncommon. Did you get TICA, CFA or ACFA papers for these cats? If so, how on earth did you afford the $600+ per kitten and yet you can't afford spaying/neutering? What about their shots?
Regardless of what breeds these kittens are or aren't if they're anything older than four months DO NOT allow them to interact. Kittens can reach sexual maturity as young as four months.
Kittens are FAR easier to introduce to eachother than adult cats. Just put them in separate rooms with their own food, water, litter. Put an old tshirt with one of them to get its scent on it, give this to the other kitten and then back again. Make sure they both are relaxed and seem eager to see what lies beyond the door and then introduce them.