NXT 1.0 software issue
I'm not sure about compatibility of different versions of NXT-G with different versions of macOS. However, regarding your second question: 

The only difference between the 1.0, 2.0, and Education NXT kits is the parts and sensors that come in the kit. There is only one hardware revision of NXT brick, and any version of NXT-G will work with any NXT brick. Thus, if you found a version of NXT-G other than 1.0 that will run on El Capitan, you could use it program your NXT bricks.