Here's a link for Los Cabos Express. We've used them before and it worked out well. Your friends will probably want to get a shuttle van just for themselves if they want to stop at the grocery store. I think some of the regular shuttle buses that stop at several of the hotels make a stop for beer, but not for groceries.
The large grocery store in San Jose that is at the interesection where the toll road joins the main highway would be a logical place to grocery shop as it's very close to the Westin.
However, be sure your friends know there is no oven in the units, only a microwave and a couple of top burners--not a full sized stove by any means. Also, I'm not sure how large the refrigerator/freezer will be in the one bedroom. They should be careful how many groceries they buy so that they don't end up with a lot of stuff they can't prepare or store easily.