Why do only Uranus and Venus rotate from East to west, while others rotate in opposite direction? Is it because of the angle of their tiltness? Or due to the process of their formation?
Venus has an axial tilt of 177$^\circ$, so it rotates backwards compared to the majority of other planets. It also has an extremely slow rotation rate of one rotation every 244 days. In comparison, Uranus rotates every 17 hours, but has an axial tilt of 98$^\circ$. It rotates in a direction almost in the same plane as its orbital motion.
It seems very likely that the planets formed spinning anti-clockwise, and then had their angular momentum changed due to interactions with other large objects in the solar system at the time. It's generally accepted now that the moon was formed when a large object impacted the Earth several billion years ago, and the remains after the impact formed both bodies. A collision of similar bodies with Venus or Uranus could have changed the angular momentum in any way, depending on the exact details of the impact, so could have led to the current state of Venus and Uranus.
Unfortunately, it's very hard to work out the details. This is because on the scale of billions of years, the evolution of the solar system is chaotic, with tiny changes in initial inclinations or positions leading to radically different results after billions of years. As an example, take a look at this figure from `Long term evolution of the spin of Venus - II. Numerical simulations', A.C.M. Correia et al, showing the evolution of the Venus spin over time. It's pretty wacky, especially near 30$^\circ$.
Current theory holds that Venus initially spun in the same direction as most other planets and, in a way, still does: it simply flipped its axis 180 degrees at some point. In other words, it spins in the same direction it always has, just upside down, so that looking at it from other planets makes the spin seem backward. Scientists have argued that the sun's gravitational pull on the planet's very dense atmosphere could have caused strong atmospheric tides. Such tides, combined with friction between Venus's mantle and core, could have caused the flip in the first place.