Assuming that the trailer will NOT be overloaded, exceeding the weight limits, which puts stress and strain on tires and bearings and springs....
You could very likely do it a number of ways, including sideways, or put a ramp up the front and drive one beyond the front of the trailer.
If you do make sure you do NOT exceed the tongue weight or risk bearing failure on the pulling machine, or bending the tongue which was not designed to have all that weight over it in front of the axle.
If you have a pickup, put one in bed of truck and pull the other in the trailer.