Ok, does this grandpa have good reviews and is he who he seems? I shouldn’t think the worst, but hey, 5 yrs of hosting does things to the mind...
If so, yes it’s a 2 guest booking. If you charge for 2nd guest - stated in your listing - then this is applicable.
I often set set up the double bed like this for 2 people (non couple) . This is from a listing In Prague that I stayed in - loved this idea as we often have 2 friends sharing a double bed. We offer them this option.