Thank you for your reply. I see now that my question was pretty vague; I guess I was hoping it would be a quick fix or as simple as changing a setting that I'm not aware of. That could still be the case, but I'm going to post a few screenshots to give you a better idea of what I'm seeing.
1. These are the Properties for the raw file in question
2. This is how I've always had my Export settings for putting digital images on a disc/USB. When I post images on Facebook, I typically Limit File Size to 2,500 K and put them in a separate folder, then uncheck the box for the next session.
3. This one is to show what little cropping was done before export.
4. The dimensions and dpi value that I gave in my original post were from the Properties of the exported photo, shown in this screen shot. I checked into that after going through Shutterfly's trouble-shooting for the low resolution warning.
I used to do contract work for another photographer who showed me how to export "High vs. Low Resolution" files. What he really meant by that (image vs. print resolution), I must admit I don't know, but I have never had an issue with how the files exported until the camera upgrade. When I look at the last session I shot with my D5500, the smallest jpg file after export is 4 MB and the largest is almost 13 MB. The first session I shot with my D810 (and the following 15 between now and then) range from 1 MB to 5 MB. I didn't really think twice about it at first because I setup the D810 the same as the D5500 and I naiively thought "more expensive camera = it knows what it's doing".
I agree that not offering prints has been a poor business decision in the grand scheme. As a beginner, I tend to over-compensate in fear of not booking, and while I have gotten a lot of positive feedback for having all-inclusive flat fees, I see what you mean about back firing, (like in this case and what is yet to be seen when the other 15 families attempt to order prints). I am willing to pay for one-on-one mentoring at this point to get it figured out because I'm terrified that my Inbox will flood when everyone else tries to make prints before the holidays!