nicely put grewal bayee, but as far as i have heard, Guru Ji ne Panj Pyaareyaan de naam rakhe nahi si, balke ohna de naam pehlaan to hi ehi si, Guru Ji ne taan bass ohna de naam naal Singh jodeya si.
First one was Daya Ram, then Dharam Dass, Himmat Rai, Mohkam Chand and Sahib Chand.
these were their original names, n they got up in this manner, that it signified the order of Sikhi.