Do all scientists believe the results of every theory?

The short answer is "no."The longer (but more correct) answer is that most scientists are reasonably willing to believe at least the broad strokes of anything that legitimately qualifies as a "theory", because by that point it's generally been shown that it explains known observations and allows the results of observations that haven't been made yet to be correctly predicted. It's sort of ridiculous not to believe something that demonstrably works. If I told you that I could roll dice in such a way as to control what number came up and then showed you I could do it twenty times in a row, if you decided to then play a game of dice against me you'd deserve what would happen to you.

However, science advances by people continually challenging accepted theories. Maybe the theory works fine for some things, but not for others. This is more or less what happened around the 1900s to Newtonian physics ... Newton's theories were shown to flat-out not work for objects that are very small or move very fast, though they're very good approximations for most objects on the ordinary human scale. Another example we're still trying to figure out is that galaxies don't rotate the way Newton's Law of Universal Gravitation says they should ... the most commonly accepted explanation for this is "dark matter" (matter we can't see because it doesn't interact with the electromagnetic force, but does interact with the gravitational force), but another possible explanation is that the Law of Universal Gravitation isn't as universal as the name implies ... it may only work at small scales, and at large scales there's another factor that becomes dominant that we never noticed before because over distances where we can actually conduct experiments it's too small to measure.