The terms for cancellation would have been in the contract for the holiday , the 3rd person will not be able to do anything about it . The other 2 can not be sued for something that was not their fault and out of their control, if this person talks to a lawyer he/she will be told that.
If anything the remaining two should sue the 3rd person for their increased cost. (but in reality even that would not work)
Tell the 3rd person to stop wasting even more money by starting a court case that they have zero chance of winning.