Are you leveling by putting blocks under the tires and driving up on the blocks or are you using the jacks to lift the 5er? You should be putting blocks under the tires to get it level side to side then use the front landing jacks to get it level front to back. Once done then lower the rears. It doesn't mater if the fronts are pinned in the same whole. They can't be when you're on uneven ground.
If you're using the front and rear jacks to level the 5th then yes your neighbor is right you'll bend the frame. And more than likely you'll toast the motor in the front jacks and ruin the rear stabs.
Now all bets are off if you have a 4-6pt leveling.