Rules were recently changed, and now demand that a guest must be on the same flight as the Star gold. You'll probably be VERY hard pressed to find two Star golds on the same flight as your siblings, let alone two Star golds that are on the same flight and are willing to guest your siblings. If you're standing outside the lounge, asking everybody what status they have and what flight they're on, you'll probably annoy people so much that they'll call security.