Okay now, this is just my personal opinion. I can't believe that your vet said it would be good enough to have someone check on them only twice a week. That's ridiculous.
Your cats are so use to having someone with them for most of the day. Can you imagine what it would be like for them to all of a sudden be all alone, day and night for a few days. Personally, I don't think this would be fair to them at all. This would definitely have an affect on them.
Is it just Amy that you are concerned with Laura? Is there a trusted friend near by that would be willing to take just Amy for you?