Just don't say anything.
Relative. "Where's the wife?"

Husband: "visiting her folks, helping out with something or other,you know. "

Relative: "sure, how long you got the place to yourself then?"

Husband: "couple of weeks give or take, depends how things go."

Relativenods) "sure, sure....So how you been keeping anyway?"

End of conversation.
On the slight off chance they ask what your doing. All your Husband has to do is look embarrassed and say. "You know, I wasn't really listening."

It doesn't have to be complicated, unless you have very pushy rude relatives.

Just go on your holiday and let your Husband deal with it.
Try and do what you are going away to do.
All the best.