Essentially there are no creditable holes in the story line. We even have witnesses reporting the right things at the right times. Hitler and Eva exited Berlin weeks before the actual end. They then made it safely to either Spain or Portugal to await war’s end and their pick up by two submarines. These craft could likely handle two each. In the meantime a disinformation program kicked in even around their escape but certainly around their apparent suicide which conforms to the execution of his body double and likely Eva’s body double.
They had plenty of time to plan this and to ensure ample disinformation was in place.
What is clear is that we can trace each step and it was all seen in some form or the other. ultimately it took an air flight to the area of the Carpathians and then a long distance hop across Switzerland and then out over the Mediterranean to fly to Spain. That avoids enemy aircraft easily as all the fighting was by then far to the North or in Northern Italy or well East.