I think they are going to be fine. Once we left Karamel for 4-5 days. He was about 4 months old then. My parents were checking up on him and playing with him. They said he was quite fine. Since its their home they will be quite comfy. Also the vet tols us you can live your cats completely alone for 2 days if you live enough food and water. And if they are 2 or more cats together they will keep each other company too. Don't worry.

Maybe it's silly but we had left a hall light on for him (It maybe needles because cats can see in the dark, can't they?)