Dejaren tries to injure/kill B'Elanna by putting his hand inside her chest. This should not be possible. Although, as a hologram, Dejaren's "body" can become non-solid, B'Elanna cannot. At most, should he deactivate the force fields that give him the ability to mimic a solid physical presence, Dejaren's hand would simply no longer be visible as it made contact with B'Elanna's body. It cannot penetrate her skin.
Janeway's primary responsibility is the safety of the Voyager crew, and yet she frivolously allows the Doctor to go on an away mission while Voyager goes on a separate mission. If there would have been a serious medical emergency, there would be no qualified medical staff on Voyager to deal with it. Additionally, since the Doctor is basically a computer program, there should be no reason why a copy of him remains aboard Voyager while another copy goes on the away mission.