There are actually three types of neutrino (and they spontaneously change from one type to another), they are all spin-one-half, and they interact with other matter only via the weak nuclear force, which has a much smaller effective distance than the electromagnetic force, so they don't interact very often. They have non-zero mass, but it is so small that we don't actually know what it is.

Everything in the universe exhibits the wave-particle duality.

Einstein's self professed "biggest blunder" was the cosmological constant. That term has never referred to the assumption of lorentz invariance.