Hello Pharny,
The 'interference' you're referring to would presumably be phasing due to playing the same sample multiple times at the same (or very nearly the same) pitch.
To help minimize that, you could, for example, set Rank.Samples_MIDINoteNumIncrementFromPipesToSamples to a slightly different value for your 'duplicate' celestes rank (e.g. set it one higher or lower than for its non-celeste version).