Family vacation

So we planned a family trip back months ago and we are renting a place and splitting the cost and we just found out the one of the people can’t go and He wants to back out of paying his share even though my husband and I have already paid for it in full and other ppl have already paid us. My question is do y’all think that He shouldn’t have to pay or that He should be responsible for what was agreed upon. Any other helpful tips on how to go about this without ruining relationships would be appreciated