It is possible, but highly inadvisable.
Yes, ships can communicate and detect between each others while in warp, but even when all ships enter warp close together it is not a guarantee that they will leave the warp near each other. In many novels, describing the movement of big fleet, you occasionally can read about "vessels lost to the Warp".
Warp is a flickery thing - conditions near your ships might be different near another, even if they are relatively close (and remember that "close" might mean thousands of kilometres).
Saying that, ships can travel without navigators with small jumps using "navigational mechanisms":
All Warp-Drives incorporate navigational mechanisms. When the ship is in realspace, these algorithms monitor the ever-shifting movements of that part of the Warp corresponding to the voidship’s current position. It is essentially a "window" into Warpspace. By means of observing these movements in the Warp it is possible to calculate a course, corrective manoeuvres, and approximate journey time to a proposed destination in realspace. Calculation relies on the assumption that the Warp-currents observed from realspace do not change significantly during flight. This method is known as a "calculated jump", but is often referred to as a "blind jump" by Imperial Navy personnel. It is not safe to make a calculated jump of more than four light years at one go. The longer the jump, the greater the chances of a significant change in Warp current movement. source
But usually there is no need for such things: Navis Nobilite is really big - their holdings span whole continent on Terra giving the Fleet lots of navigators to choose from.
You could compare it to the sailing on the ocean from the time of Columbus: You could either do safe hops near the coastline or go deeper into ocean with skilled navigator using maps, compass and sky. While you could get a group ships to blindly follow the leader, they could get easily lost during the storm and without means to find their position, they would be left at the mercy of the ocean.