to open KR and 2D at same time, you have to start 2D first (especially if using UOA), then start KR without client patching, by starting the UOKR.exe file directly.
Be advised though, that doing so typically lags both clients to hell. It's best used only for things like having a tamer on one account rez the other account's pets, guilding characters in the other account, trading houses, etc.