@Lisa6023
The fairest way to handle this situation is for the person who organized the occasion to accept full responsibility for the cost. If someone in your family happens to be struggling financially, it would be rather callous to force them to choose between spending more than they can afford or being excluded from a special occasion with their loved ones.
The second most fair solution would be for the organizer to create a group holiday fund that each participant voluntarily pays in whatever they are comfortably able to contribute at the time, and choosing the accommodation and other expenses based on the resultant budget.
Splitting the bill evenly per-person may seem superficially fair, but it doesn't account for the disparities between people's incomes, the differing expenses they incurred to get to the destination, and the varying amounts of space and privacy they'll all have in the accommodation. Many times, I've watched a group at a restaurant try to split a bill evenly when some people ate several courses and ordered expensive cocktails while others just had a salad and tap water. If you're one of the ones who just got the salad, you'll probably never want to dine with those people again.
If the stay is already booked, a bit of backtracking may be in order. But in general, anytime you invite people to something you expect them to pay for, I recommend involving them in the budget discussion before making the arrangements rather than springing it on them after.