I would try the jacks first, before lowering the tire pressure. Lower the front jack, that came with the trailer, down so that the rear is about 2" higher than the front. Place the jack stands you bought, under the rear, and then jack the front back up to level. This will preload the rears. Install the front jack stands and then install the extra stands in the middle. That should be plenty to stabilize the trailer.
Don & Mary
2019 Newmar Dutch Star 4018 - All Electric
2019 Ford Raptor Crew Cab