What are the qualifications to be my dads power of attorney?

do i have to have my own car even if i can still get him to dr. appt. w/o one? my mom which has POA over my dad is very emotionally abusive to him, and other issues are present as well. my dad is very capable of communicating and has a clear mind now a days so he can speak his concerns to SSI when we go . so if he wants to change POA to me, is it that easy? we think trying to proof himself competent would be to difficult legally speaking so switching to me would be easier. any suggestions or input?