I think immunity was the thought on the HMs minds.
After all, if you put in people who are not going to be nommed anyway, that's not actually a real benefit. Apart from the "luxuries", Sam and Sophie haven't got anything of real value.
I think all the HMs who are not in the (un)safe house will react with a mixture of shock and relief when they find out the truth. Some of them may even weep and apologise to the safe house trio, whilst laughing up their sleeves with delight at finding out they're immune!
