Dear if it is visit visa return ticket will b necessary for them to come out their country and also to come in to this country. even if u go to buy them ticket they wont give u one way as its visit visa n nt residence visa.. so the better choice if u have a friend working in any agency like etihad or anything try to ask him to provide u two ways ticket then u will pay only one ticket and other ticket will be canceled once ure family reach qatar i mean u will call him n ask him to cancel it once they r here. thats wht my husband did for me.. hope this answer wil help u out.. wish nice trip for ure family.