Do you need to reply to the holiday greeting message sent to your elders after receiving the reply and blessing?

There is no need to reply, especially blessing messages. Once you send it, it doesn't matter whether the other party comes back or not, because you send a blessing. If the other person wants to express his blessing to you, he will definitely give you one back (this is also a courtesy). If the other party doesn't ask questions in the reply, you don't have to reply again, otherwise it will be tedious and verbose, so it is enough to express the sincere wishes between the two parties thoroughly.