Liability for injury to party guests during and after the party

Am I or my sister legally responsible in Saskatchewan for any misfortune befalling guests at a party held on my sister's property by my daughter for some of her friends? She wants to have a weekend all-night party on my sister's acreage/farm and of course there will be alcohol involved. It may not be possible to contain some of her guests, who may choose to drive away intoxicated. If they are involved in an accident on the property or off the property on their way home, am I or my sister liable for damages? The guests will likely be 17-19 years of age but who knows, some of them may be younger...I don't know whether to give my permission for this event or not - do you have any advice from a legal point of view?

Yes you can be held liable. You may want to review this with your insurer as well as a first step.