You need to tell them directly yourself as I think your DH is very worried about being the bad guy.
Not sure about this. Suspect it's more likely that DH said yes out of feebleness, & without considering not just the CF-ery, potential consequences, extra work, & certaonly not his wife's feelings.
Now his wife has pointed out her feelings to him, he doesn't want to back down or admit that this pair are CF's, & is making himself feel better by laying the law down to OP - because at least he can do that, as Man Of The House, huh?
OP is probably overwhelmed by the volume of PP's highlighting this, as she has posted that she has spoken to DH about it again & that he refuses to budge - but I don't think she has updated since that ..?
So there is little point admonishing her to enact passive-aggressive little rebellions such as leaving notes, asking for money, playing games with toilet rolls & linens to make CF's stay awkward - because if she feels unable to challenge her DH on something so fundamental as this unwelcome visit, she's hardly going to feel confident to effectively challenge him further by tackling the CF's direct. That clearly includes ringing them up to tell them they cannot stay in her empty house. It's pointless to keep urging this - & it's not even the main issue, which is her DH's casual disregard.
OP - it's concerning that you feel you would rather cave in & endure the discomfort of having these people in your house while you are away than stand your ground with your DH.
It is not normal for one member of a couple to over-ride such a basic decision about the shared home.
It seems that you have decided to go along with DH's decision, to keep the peace. Does he usually expect to be the sole decision-maker in your marriage? Does he make sure he is the one who calls the shots on matters like finances, or childcare, or the split of domestic & money-earning roles?
Maybe you are going to just let this one go, upsetting as it is, & allow your DH to dictate what is allowed in your home, despite your obvious discomfort. But please have a think about the power dynamic it has uncovered in your marriage, & how much more of it you are going to have to put up with. This is kindly meant but - if you give in on this issue, you will have effectively told DH that your opinion is worthless, does not need consideration, & that he can ride rough-shod over you without consequeces to himself.
I would be far, far more concerned about that than the CF's whose request has opened this can of worms.
God luck OP. 
Good luck whatever you decide, & please think hard about what this episode has revealed to you about how DH expects to treat youm & how he expects you to respond.