In your case given the equipment, I would opt for a LONG chain and pull them over, at least that way for the bigger ones. Chain needs to be longer than tallest tree, dont want them falling on you. Hook the chain to the pulling drawbar, not to the 3 PH arms.
With small saplings, you might try pulling them up with the 3 PH arms by using a drawbar that fits in the lift arms. Back up against the tree and hook up your chain low as you can then lift the 3PH to pull them up by the roots I have done this using an old 8N Ford years ago. Lots of on and off the tractor, but it works. These are small ones that you can physically push them over after your pull them up so they dont fall over on you. Works better if you have a partner to chain up the tree each time.
I pulled out a bunch of sweetgum saplings 3" and less in diameter with my Kubota RTV 900 using a long chain. A lot depends on the root system, my sweetgums didnt have much root and usually snatched right out. I used the RTV as it was more maneuverable and easy to get on and off.