Native English speakers: grammar question

[Ghostmojo]

Hi,

someting that came up in an English test of our son and which we are not quite sure of - could I please have your opinion on the tense to be used with the following sentences:

Mr A: "Have you seen the Leinerts?"

a) Mrs A: "No they have left the house in the morning and I think they aren't back yet."

or:

b) Mrs A: "No they left the house in the morning and I think they aren't back yet."

Which one is right, or are maybe both ok?
Thanks for your help!

I don't think I would say either to be quite honest!!! With me, and most people I know, I reckon it would be more like:

c) Mrs A: "No they left the house this morning and I don't think they are back yet."

It's the final part of the phrase (which I have underlined) that sounds most odd to me ... besides which, you'd have to search long and hard to find a surname like that within 50 miles of here! Probably much further ...