I have the same case, my sister will come here next month from Jeddah as personal visit visa. As far as I know, return ticket is a must. If she's planning to look for a job here, better, ask your travel agency if they're issuing dummy ticket for the return ticket to Phils. For stamp on his passport, I'm not so sure, but a person from travel agency told me that, Qatar Immigration will only ask for passport/copy of visa.

http://www.qatarliving.com/answers/visas-and-permits/personal-visit-visa...

Good luck =)