From your post on castration, I'm guessing that your current pigs will be about 6 months when you get your 8 week old weaners?
Others know much more than me about this - we've never had KK - but a 6 month old Tamworth is an awful lot bigger than an eightweek weaner. I would thing that bullying, especially at feeding time would be a real issue. Personally, I wouldn't mix them - certainly not right away. They might be OK if they could see each other for a while before actually being in the same pen, but even then...
Still, lots of experienced pigkeepers on here who will advise.