Mahto and Yadav, who were reportedly charged with minor offences, were claimed to be serving Lalu as helper and cook.
RJD leaders attacked PM Modi and CM Nitish Kumar, alleging that it was a malicious exercise.
The party's state unit president Jagadanand Singh announced the names of Mohd Qari Sohaib, Munni Rajak and Ashok Kumar Pandey.
The 31-year-old is seeking re-election from Raghopur in Vaishali district which he had wrested back for his party from the Bharatiya Janata Party's Satish Kumar in 2015. The BJP leader had defeated Yadav's mother Rabri Devi, a former chief minister, in 2010.