I'd say, rather than worrying about the quality of your digital glass at your level, get a big card (Well, more memory. Smaller cards and plenty of them can be better up to a point) and more batteries. What you know well, do that. A lot. Make up cards that you can hand out directing people to like a Flickr album to post what they get. (And go ahead and dedicate it to the grandma, that does good honor,
) . Everyone out there has point and shoots, these days, (And unlike when I was in the business, they tend to work a lot more often) so make a place to compile them online.
Make it participatory instead of putting it all on yourself. It'll add to it all rather than make you worry if you pass muster.
I'm sure we'll all try and coach you as we can. In general, try and stay in the middle of your kit lens' zoom range and a moderate aperture. (A smaller external flash made for Pentax would help you there, )
Just the kind of case I might be tempted to take on, if I were in range, though. Not something I do anymore for money.