The thing about people that are trying to have a good time is that they can often end up being pretty irresponsible with all things having been considered and taken into account. The reason behind this is that they are not thinking about their health in any major way, shape or form, which is why you as the host need to make sure that they are trying to counteract their booze intake by helping them consume some other things that are also going to be useful for them and are going to allow them to party pretty hard without passing out before everyone else is done having a good enough time.
You should try your best to keep everyone hydrated on your party bus. A lot of party bus companies in atlanta have water coolers on them for this very reason, but the fact of the matter is that people might not be interested in water when there are so many more enjoyable things that they can drink. This can lead to them getting really dehydrated though which means that you might want to keep giving them water otherwise there is a good chance that they would throw up.
Just one person throwing up at a party can spoil the mood for everyone else especially if they threw up on the floor of the bus in question. People should take care of themselves but you should also think about their wellbeing since you are the one that invited them and are therefore responsible for making sure that they don’t get sick to a certain extent. Try not to be too forceful though as this might just end up annoying a lot of people.