Why aren't satellites disintegrated even though they orbit earth within earth's Roche Limits?
The Roche limit denotes how close a body held together by its own gravity can come. Since gravity tends to be the only thing holding moon-sized objects together, you won't find natural moons closer than the Roche limit. [Strictly speaking, the Roche Limit is a function of both the primary (in the case of this question, Earth) and the secondary (satellites) bodies; there is a different Roche limit for objects with different densities, but for simplicity I'll be treating the Roche Limit as being a function just of the primary.] For instance, Saturn's rings lie inside its Roche limit, and may be the debris from a satellite that was ripped apart. The rings are made up of small particles, and each particle is held together by molecular bonds. Since they have something other than gravity holding them together, they are not ripped apart any further. Similarly, an artificial satellite is also held together by molecular bonds, not internal gravity.
The molecular-bonds-will-be-ripped-apart-by-tidal-forces limit is obviously much smaller than a satellite's orbit, as we, on the surface of the Earth, are even closer, and we are not ripped apart. You would have to have an extremely dense object, such as a neutron star or black hole, for that limit to exist. Being inside the Roche limit does mean that if an astronaut were to go on a space walk without a tether, tidal forces would pull them away from the larger satellite. Outside the Roche limit, the gravity of the larger satellite would pull the astronaut back (although not before the astronaut runs out of air).
If you look at the influence of the Moon's tides on Earth, you can see that the oceans are pulled towards the Moon, but the land is (relatively) stationary. The fact that tides are only a few meters shows that the Earth is well outside the Moon's Roche limit (and of course, the Earth's Roche limit is further out than the Moon's, so the Moon would reach the Earth's Roche limit long before the Earth reached the Moon's). If the Moon were to move towards the Earth, the tides would get higher and higher. The Moon's Roche limit is the point at which the tides would get so high that the water is ripped away from the Earth. The land would still survive slightly past that point, because the crust has some rigidity beyond mere gravitational attraction.
Regarding your second question: there is a region in which the tidal forces would be larger than internal gravitational attraction, and a region in which internal gravitational attraction would be larger than tidal forces. The Roche limit is the boundary between those two regions. Everything inside the Roche limit constitutes the former region, while everything outside the Roche limit constitutes the latter.
The Roche limit applies only to bodies which are held together purely by internal gravitational attraction. Compact objects such as artificial satellites are held together by the much stronger inter-molecular electromagnetic forces (this is another demonstration of just how weak gravity is compared to electromagnetism).
As for your second question: the Roche limit usually defined as the radius away from a body at which magnitude of the tidal forces exactly equal that of the internal gravitational attraction of the smaller body. Of course, the magnitude of the tidal forces becomes significant at further radii, and so the distance at which tidal forces become significant is a much broader area/range.
The Roche limit is a limit on objects being held together by their own gravity. Satellites are held together by much stronger forces. Different parts of the satellite are ultimately connected by chemical bonds, which are electromagnetic.