What kind of visas are required for parents visiting USA?
The kind of visa required for parents or relatives to visit US is Visitor Visa (B2) visa.
What is the process for applying visitor visa for parents.
Look here for complete step by step Visitor Visa Application Processfor USA
What documents required for visa Applicant parents?
See list of required documents for parents for US visa purpose visit Visitor Visa Documents.
What documents required for Sponsor for us visa for parents?
See detailed list of requirements for sponsor documents for USA visa for parents.