So scenario is you have two non-status pax on a different PNR, flying internationally? They each get one free bag @ 50 lbs, you get 3x @ 70lbs. You want to check up to 4 more.

As others have said, agent is likely to let you check 4 more (2 per pax) without charge, but no guarantee. No real way to guarantee this before you're stuck.

As for 9 bags, we wrangled that many for child's trip to college movein. Those cheap vinyl bags from Amazon (or Ikea) are great for this - they stack neatly.