I think the stress of moveing them quick will end up not being the best for him. He should get the levels in his 150 back to normal first and then move them. They could go into shock by such a difference in water quality, and he could lose them.
Do exactly what DavidW has just said. Tell your friend NOW!!!! The only thing i disagree with is i would keep a thin layer (less than 1") of sand.remove the sand from the new tank and go bare-bottom, it is easier by far to keep clean.
move all the fish into the new big tank...acclimate them for about an hour.The water they're coming out of and the water they're going into is the same except for the ammonia etc levels. then move all the filtration from the old tank to the new tank, give the filter media a quick rinse in tank water, not to much, just enough to remove the crud.
then add about DOUBLE the filtration you already got.
Cycling a tank is about getting a new filter started up...as you will be using the old filtration that is not an issue.
Do this today....ammonia is the cause of 'silent death'with rays...don;t be surprised if in about 2 weeks some of the rays die.
DO NOT ADD ANY NEW FISH just because the new tank is bigger.
Rays and Arows produce huge amounts of waste and you have enough fish for now.
Then change 30-50% water every other day...get test kits and test daily for ammonia and nitrite