So I worked out a bunch of issues in the last couple of days.
1. In trying to solve the issue with Image downloading from the details window, I explained before I had to copy the plugins. But while that worked on my computer, it did not work on my wife's computer. I found that the reason why was that they were pointing to libraries and files in the INDIRoot folder which was on my computer not hers. So I added those plugins to the list of files to be run through the Install_name_tool.
2. In exploring the problem above, I finally found out that it would be better to use @loader_path instead of @executable_path in that tool because Jamie's script determines the location of the dylib files from the file it is running the install_name_tool from, rather than the executable that is running that file. In other words, while the @executable_path works great for direct dependencies of executables, it doesn't work for the dependencies of dylibs. @loader_path would then use the path from the executable or the dylib, whichever called on the dependency. So I changed that in the script.
3. Then I discovered the reason why I was having trouble with libindi, libnova, and libcfitsio files being copied into the frameworks folder. Jamie's script was using this command to find them: filename=$(find /usr/local -name "${base}"). The problem is that it was returning multiple results, so when you tried to use the cp command, it didn't work because the string for the filename contained multiple files. So I modified it to take the first one it finds. We might want to change this later, and it may not be the correct way to do it, I don't know, but for now it seems to fix the problem. filename=$(echo $(find /usr/local -name "${base}")| cut -d" " -f1)
4. After that, I decided to try working on the dmg to make it pretty. So I used this website as a reference and modified our code at the end of the script to make a nice dmg.
community.kde.org/Marble/MacPackaging
I now have a great working dmg that I built on my old Mac that should work perfectly on both newer and older Macs!
Note, that this was built with my old Mac running El Capitan. If I try to run Jamie's script on my new Mac, it also produces a dmg that mostly works great on both my new and old Mac and my wife's computer. But if I try to connect to an indiserver and take an exposure, it still says Illegal instruction:4. Which means something somewhere is not built properly for older versions of the OS I think. But regardless, we have great progress. A fully working dmg!