In SDR could you isolate I and Q
Yes I and Q are in quadrature and therefore orthogonal so they are naturally isolated. For example you could consider QPSK as two independent BPSK channels transmitted on the same carrier frequency (or you could consider it having twice the spectral efficiency as BPSK since you can send twice as much data at once within the same bandwidth, and at the same SNR level).

To maintain isolation in the SDR you need to have good IQ balance or correct for IQ quadrature and amplitude error. Correcting for analog errors with software as depicted in the diagram below is easy to do: if the data content is equally distributed in the long term then the data can be used directly, and this would be a reason to "whiten" the actual data with scrambling prior to transmission. Otherwise training sequences could be used for such calibration of the receiver hardware- to the extent that is needed to be sufficient for audio purposes. Amplitude is adjusted by comparing the rms magnitudes of I and Q, and phase is adjusted by correlating I and Q (average of the product of I and Q over all samples) and scaling by the amplitude (to get phase).