The following are my responses to your questions:

"Can a sibling take guardianship of a physically impaired brother although he is married and the wife is providing care for him?"

The sister can petition a court to have her brother deemed incapacitated and to have herself appointed guardian. However, she may not be aware that guardianship is a lengthy and expensive process. Additionally, there must be a finding by a three-person examining committee that the individual is incapacitated.

"...take legal guardianship of brother so he could see kids regardless of R.O. Can she do that?"

The sister cannot circumvent a restraining order by being appointed guardian of her brother. She will have to honor the restraining order in place.