If you are going to change the pins with a different type of steel your best bet would be to use stainless steel.
Much harder than nickel silver and less chance of corrosion. Brass would be way too soft for movement points like pivot and center pins.
But there will be a color difference.
Steel pins are fine to use as long as you maintain the knife with cleaning and oiling regularly.
If you don't want to see the pins then use the same material that the bolsters are made of.
You can use any metal on the other fixed pins.
Here are two examples both using stainless.
One knife with nickel silver bolsters and the other with brass.

J W