Jack stands & a 12 ton bottle jack are relatively cheap.
Start with trailer still on the truck. Crack all wheel lugs loose. Lift one side just fwd of spring hanger. With both wheels off the ground, jack stand just aft of spring hanger. Don't remove wheels yet. You want them there as insurance just in case something slips as you repeat the lift on the other side, same way.
Getting to this point you will have tipped the trailer fwd placing more weight on the 5th wheel. The landing legs may or may not be powerful enough to lift the front high enough to get the truck out. No problem. Use the jack to lift & extend legs so that there is no weight on the truck at all.
At this point the truck can be removed without any pull on the trailer at all & the trailer is as solid as a house on the ground. Now the wheels can come off.