As there is no contract between you and your sharers, then it is doubtful there would lie any legal actions. You have no contract as the courts do not prima facie agree that social arrangements are intended to create a legal relationships. If they give you money, you may do as you wish with this as this still does not form contractual status...and equally, you have no legal claim to continued payment. Thus, you are still only carrying passengers and do not require any extra insurance. A passenger could sue you anyway in the event of an accident, but only if your driving is negligent would you be blameworty. Plus, the courts have taken a dim view of claims where a person enters the danger willingly, but then cries fould when harm occurs.
I don't know about holiday breaks, sorry, and this answer assumes that this arrangement is only semi-formal i.e you do it as a matter of courtesy and may withdraw if inappropriate. Hope this helps.