I am not that familiar with your exact set up, but I can tell you manufacturers mix 8 ohm and 16 ohm and other impedances all through out history with no ill effects.

Yes, the crossover is designed to take this into account. No problem.

Before you do anything, check to make sure that all you drivers are working properly. If both low drivers match, both high and mid drivers match in pairs, then all should be fine.

BTW, matching drivers could easily be ten to fifteen percent off from each other in impedance and still work fine as a stereo pair.

If I was going to look for something to TWEAK your vintage speaker systems a bit, I might think of upgrading the actual crossover components with modern higher quality components, using similar value parts, to start with.