We describe the JHU 189 atlas here

  https://www.ncbi.nlm.nih.gov/pmc/article...

by citing this paper

  https://pubmed.ncbi.nlm.nih.gov/22498656...

The ch2bet is based on a single individual and is described here:

  https://www.mcgill.ca/bic/software/tools...

While I am happy that my classic MRIcro and MRIcron tools have proved mature and popular, please understand that my development efforts focus on modern graphics hardware  resulting in MRIcroGL and NiiVue. Personally, I prefer the mni152 and spm152 templates provided with MRIcroGL. These are based on the 2009 atlases with MNI size (larger than average) and SPM size (average) to match the most popular normalization atlases:

https://www.bic.mni.mcgill.ca/ServicesAtlases/ICBM152NLin2009

For details on these two sizes, see:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6050588/