I know this is a very old thread, but I did run into this issue of the "arbitrary member chosen for the skill check", and I've realized why it happens. At least it applies to all the times I've encountered this so far.
When multiple characters are selected, choosing to interact with something a little far off will often have just the nearest character go all the way while the others stay. Then, when the character interacts with it, the storybook section will only have them as an option. Cancelling out and bringing everyone close does it.
