legally take guardianship of brother

Hi all,
I have a query to post. I lost my mother last year suddenly due to cardiac arrest. I have an married elder sister and younger brother. I take care of my younger brother, he is mentally challenged. I am thinking of taking legal guardianship of my brother. I am not very sure why I need this but some how I feel that if I have to take his ownership from all the perspective for medical grounds, travelling etc..
Can you all suggest what can be the pros and cons of doing this?

Thanks in advance...