If you were concerned about tactfully preserving your friendship with these people, the situation would be more delicate than it is. It sounds like they are totally not friends and not people you are going to go out of your way to keep in your lives from now on.
Nevertheless, I would be a little more tactful than what OBXBRIDE suggested. I'd just tell them that you've been reviewing your plans for the wedding and have decided, for a variety of reasons, that you need to have fewer attendants so you would like to relieve them of their obligation.
It would be good for you and FH to rehearse this a few times so that you both give the same line of reasoning, now and for the future. Even if this friendship is not to continue, there is no harm in presenting it discreetly so that if the "un-asked" couple blab about you to others, and those others come and ask you about it, you will tell everyone the same thing.
"When Women Vote, We All Win!"
EveT
Llama Jjammies
