Okay, so you're saying in my picture where I have it labelled to use 75 ohm coax, you would use 50 ohm coax to feed both antennas for the 1/4 wave and 1/2 wave pieces etc?
Then the input of the coax switch would be 25 ohms?
If I use two 1/4 wavelength pieces of 75 ohm coax in parallel between the rig and the coax switch, that will be 25 ohms at the antenna switch?
Assuming the two antennas are 50 ohms (though a quarter wave whip may be
lower than that.) The two 50 ohm loads connected in parallel give 25 ohms, just
like two resistors in parallel. Technically you would want a 35 ohm cable to match
25 ohms to 50 ohms, but two quarter wave pieces of 75 ohm coax in parallel should
get you close enough.