MH is strong (you can see his biceps in the hearing video) and his history of using a gym and climbing trees. His former employer said he had his own climbing gear, which would probably include ropes, harnesses, pulleys.
I think even LE was mentioned as saying that MH used harnesses to pull the bodies up to drop them in the tree.
Even a somewhat weak person could do this with ropes, pulleys, and a ladder. But I think MH didn't need a ladder. He could rig the body (put it in a harness or wrap it in rope), climb the tree, throw the rope over a strong branch, and pull the body up to him and drop it into the hole. Repeat 3 times.
What he did was diabolical, but this part was probably the easiest since he very likely had the right equipment.
Someone posted upthread about rigor mortis, and that probably made it easier (as long as he had a tree with strong enough branches above the hole, and a hole that was high enough off the ground.
Since all of this was accomplished, he had whatever it took. So therefore, by overtaking 2 adults, 1 male preteen, and a dog, with no accomplice (according to LE), having "the perfect tree" in a somewhat remote location, there's no question in my mind that it was premeditated.
I wish we were talking about a movie and not real life.