Nyna, please don't be afraid to hold her. They are not as viscious at night as they act in the daytime sometimes. They cannot see at night and usually just purr because they are scared. When you go to get her, take hold of her firmly on her wings. Pick her up and hold her close to your chest (this will keep her calm). Have someone else apply the vaseline and then place her gently on the roost (making sure her feet are set, so she doesn't have to flap). The others shouldn't move if you move quietly and gently. If they're familiar with your voice, sometimes it helps to talk to them so they know you are coming and you're not a predator.
Getting them off the roost at night is the best time to get to know ones that don't like to be held.
I don't want to recommend treating the roosts because so many things can go wrong with that. For one, they could slip and fall - someone could get hurt. Plus their feet are sensitive to bringing in bacteria, so don't want to risk anything unnecessary. Although you will likely need to treat the roosts with something while they are out to eliminate the problems (i.e. diluted bleach solution or mite spray).
Jody