For which aircraft are you speaking? Each aircraft is going to have a different glide ratio and best glide speed. Altitude is going to determine best glide range and endurance. Either way, any assistance aircraft would have to be on station at the time engine loss occurred.
Now, for arguments sake, let’s consider an average military transport aircraft. A well trained and equipped group of paratroopers can completely evacuate an aircraft in less than two minutes with no more than two minutes advanced warning. That is if they were suited up before the emergency ensued. If they were not suited up, an in-air donning of all the gear for an entire plane load may take ten minutes if all of the parachutes were palletized. Five minutes if each person were already carrying the gear in hand. That would include buddy checks and maybe jumpmaster checks if enough jumpmasters were present. Having done mid-air parachute donning, I know that it is possible. Having not done it in an emergency, I have been conservative on my estimate of the time involved. I also have not included any time spent by the pilots scoping out an appropriate or safe LZ for the paratroopers. Nor time spent racetracking a pattern around the LZ to line up for the right distance and direction for favorable wind drift.
This would be the bench mark for a rapid emergency deployment. It would be the best scenario if flying at low altitudes. If flying at higher altitudes, like those normally flown by airliners, it may be wiser to try to glide down to a nearby airport with all personnel still onboard. It depends on the circumstances. Considering a safe LZ for an entire plane load of paratroopers would be a clearing at least a mile long and an eighth of a mile wide, a safe landing on the same field may be possible for a military aircraft with STOL capabilities.
Now, saying all that, my only real mid-flight emergency came as a passenger paratrooper in a C141 over the Pacific. The pilots opted for a glide to Oahu for a dead-stick landing. We had three other C141s in echelon. Since only a few of us were awake at the time, most of the other paratroopers were not even informed of the emergency until it came time to prepare for landing.
Using that as an example, can you imagine the possibility of doing the same with one to four hundred civilians with no prior training. The weight and space (mainly space) required for the parachutes would eliminate the possibility of carry-on luggage other than personal items. Then, the jump itself would be a complete cluster. The possibility of a complete evacuation of a fully loaded commercial airliner in the time remaining for the glide would be slim. Especially since the jump would need to be performed below twenty thousand feet MSL. Even if you were using parachutes with AADs. Especially if you were using static lines. Above that, your time of useful consciousness without supplemental oxygen goes down to as low as five minutes and continues to decrease to mere seconds at the altitude that most airliners fly.
Again, this is the best case scenario for a commercial airliner. Given the above conjecture, it would make some type of Hollywood style plane-to-plane transfer of passengers darn near impossible in the glide range of most transport aircraft.