If you can find a copy of the Gregory Heisler book, I really enjoyed it. It’s not so much about apertures and f-stops but about how he approaches specific subjects. Looks like it’s actually only $5 on Kindle right now, so if you have an iPad, that might be a great pickup. It’s called Gregory Heisler: 50 Portraits: Stories and Techniques from a Photographer’s Photographer
If it happens every year, I’d just bake it into my schedule since I know it’s gonna come up. I’d streamline the process as much as possible by telling them “Hey, I don’t have a lot of room in my schedule this year. I can meet all of you at TK place at TK time for a half-hour and squeeze everything in. Dress seasonally and be on-time because I have another engagement after that I can’t be late for. Looking forward to it!”