Don't mix them, and don't use silicon
Statement: Polyglycol brake fluids corrode the braking system
Polyglycol brake fluids (like DOT 3 and 4) are hygroscopic. When they absorb water they tend to destroy the rubber bits in the brake system. Solution: Bleed once a year. Empty the master, refill with clean fluid, and gravity bleed each caliper until you get nice, clean fluid out. I bleed mine at least once every six months on all my vehicles. I have a 1996 Chevy Astro with 94,000 miles on it. I changed out all the brake parts, including flex hoses, for an extended road trip in 1994. Disassembly showed that only the wheel cylinders looked a bit sad. Other than that I had replaced no parts but shoes and pads.
Statement: Silicon fluids corrode the brake system.
Since silicon based fluids do not absorb water, condensed water can pool in droplets and corrode aluminum and non-stainless parts of the braking system.
"Mixing" isn't wise since they really don't mix. Sort of like oil and water, you can get them together but neither will be happy.