Here are a few resources that could help you all think about your brother’s move.
You might be interested in the Reach standards. These aren’t a detailed checklist, but might go some way to helping you all think about whether the setting really works for your brother: http://qualitycheckers.org.uk/about-aqc/quality-checking-tools/the-reach-standards.
It sounds like you’re already familiar with the checklist from Age UK here: http://www.ageuk.org.uk/home-and-care/care-homes/finding-a-care-home/#whattoask. As you say, it’s designed for older people, so will not all be appropriate.
There is also a checklist on the United Response website here: https://www.unitedresponse.org.uk/support-guides. It asks questions that would help when choosing a support provider.
The referral checklist here: https://www.unitedresponse.org.uk/transforming-care focuses on people being discharged from hospital who may have behaviour that challenges, but may also be of interest.
Finally, pages 13-28 of the NHS England service model (again particularly developed for people with behaviour that challenges) gives a series of statements of what people should look for in care and support: https://www.england.nhs.uk/wp-content/uploads/2015/10/service-model-291015.pdf.
I hope that one of these is useful, and that your brother’s move goes really well.