Yes, the tombs were well hidden almost immediately after their construction. The entire reason for moving to the "Valley of the Kings" was the fact that earlier Pharaohs could not prevent the robbery of their pyramids. Even under day-and-night guard by soldiers, a pyramid was a huge beacon which essentially said to the world: "Yo! Loot's here!" Inevitably, they were all ransacked. Therefore, the pharaohs of the Middle and New Kingdom started moving more and more towards deep, rock-cut tombs. The nobility had already been using such tombs for some time beforehand, so it was not a completely new technology - it was just new for the royalty to be buried in that fashion.

Along with the rock-cut architecture (which grew more complex over time), the builders began to include features like false doors, "diversion" chambers (containing lesser treasures to distract thieves), booby traps, and pitfalls where robbers would plunge to their deaths. In short, security was the major driving factor behind these tombs. The entrances were also well-hidden. This helps to explain why Tutankhamen's tomb was discovered undisturbed. To answer your other question - the living did interact with the dead a lot in Ancient Egypt - but they did not visit the tomb itself. Instead, they visited a nearby "mortuary chapel" with an image of the deceased pharaoh. Royal mortuary chapels could be very lavish.

In the chapel, the dead king's descendants would offer fruit, beer, grain, flowers, and other offerings to ceremonially "feed" the dead, who were believed to revert into "hungry ghosts" if their relatives failed to appropriately honor their memory and support them in the Afterlife. Recall that the Egyptians believed that the Afterlife was a blissful, heavenly state of eternal life which was very much like life on earth. Therefore the dead still required many of the necessities of life such as food and drink, albeit on a different scale/timeframe. This essential function was performed at the mortuary chapel, allowing the tomb to remain hidden and undisturbed. Unfortunately, as I am sure you know - even the Valley of the Kings was eventually picked clean, except for King Tut. The rewards were too great. Even though the builders were sworn to silence, they were not immune to bribery. Often, the builders would lead robbers to the hidden tomb location in exchange for a share of the loot.