Family can join straight away..i had mine coming with me since day one..but bear in mind,if ur family eligible for visa on arrival, they do need an exit ticket to get the tourist visa but if ure lucky u can get thru without one but still u will have to buy one eventually cz tourist visa only valid for 60 days max and QR only provide one way ticket for joining..u can start to apply for their RP once u get urs..u need to get ur family really clear on the situation tho to avoid them bugging u during training..they might get bored after couple of weeks in Doha and start to bug u to entertain them..