Fish that size I would tend to just put in a chilly bin (or poly box) each, no bag. I have transported fish that way but if only a poly box, it will tend to leak around the lid, even if it is taped down!
You could also try the Plastic Box or similar for large containers with leakproof lids.
1/3 max water to 2/3 air. Don't feed the fish for a day or 2 before travel (less poo). I would also have another container of aged water so I could do partial water changes if necessary. Don't know if you are making the trip with them in 1 day or stopping overnight. I have travelled from Blenheim to Dunedin with fish bagged over 12 hours with no problems. One of our members bought a discus from Wet Pets in Palmerston North, got it to our place, stayed the night, then continued on to ChCh the next day. Fish survived with minor water change at our place just to be on the safe side.