Also If I change the 50K into 10K each will it not adversely affect the channel separation?
No, the virtual ground at the opamp input takes care of that.
However as the pots are 50k you certain do not want to load them with 10k or 4k7, ideally they
would not be loaded at all. With 10k you'd severely distort the linearity (or logarithmic response if
the pot is log law). It would actually be better to use 100k for that reason, although
high impedances have issues with pickup and noise. The existing 50k seems like a not unreasonable
A better approach overall is to buffer pot wiper voltage with a unity gain buffer, then the summing
junction resistors can be a nice low (ie low noise) 1k or whatever. For a low noise microphone preamp
you'd have to pay close attention to such issues, but that's not the case here of course.