The travel agency signed up and paid the money. I can't go for some reason. Can others take the place of traveling?

If you leave the group a few days in advance, there is basically no loss, and you can get a full refund. If someone else is allowed to go, these things are irreplaceable except international routes or air tickets, and only a loss can be made and other expenses refunded. More detailed information can be consulted on the poor play network.