I think they just got really lucky and didnt have to deal with half the crap we did. Think about it, if they ran into some bandits instead of our gang on the train, they would probably have been shot. They were far too trusting and far too quick to accept us into the gang. Im not even sure if they had guns when we first met them and if they did, they should have been pointed at us.
Numbers means that you're group can have a variety of skills. The group with more people is more likely to have doctors, mechanics, fishermen, hunters and simple fighters. Also if you run into a group of bandits, numbers would make a huge difference. Provided you have the right people in you're group and they work together well, the more the merrier.
Also, welcome to the forum