shvl73
As far as removing the trees is concerned, consider using a backhoe. You will need to remove the majority of the rootball if it is under any concrete, foundation, or area where future settling woud be a problem. If you just cut them off, and grind the stumps down, the rest of the tree under your building will eventually rot, and leave a void that can cause lots of problems. If you dig them up and get the major roots out, you can fill the hole back in with structural fill, (roadbase, recycled asphalt or concrete), compacted to give you a good firm surface to build over.
If you decide to try pulling them out, cut the top off about 5' above ground first, that way you still have good leverage to pull with, but don't have 20' of tree falling on your head when/if it comes out. Also allows you to use much shorter chain, less chance of whip over if it comes loose. Do not use a nylon tow strap. They stretch and can be very dangerous if they break or come loose under load.
Also, consider clamping a couple of pieces of stout steel angle or box stock across the back of your rops to act as a shield should something come loose and snap back at you.
Be careful and have fun.
DT