Rich: The split will be less of a problem if you can fell the trees in such a direction that the split in each one is perpendicular to your notch cut and felling cut. Let's say the split runs north to south. You wouldn't want to fell the tree to the east or west because your felling cut would be cutting completely through the split, allowing the tree to act more like two separate trees than one single tree. If you fell it to the north or south, the split will be bisecting the section of wood that will be acting as your hinge, which is not a big deal since at the present time the tree is strong enough to hold itself together, and will remain so as you are felling it.
Since I'm not sure how well-versed you are in felling trees, I'm going to run the risk of telling you something you already know by stating the basic principles I use in felling a tree. (There are some variations to the following guidelines for special situations, but these procedures will work in the vast majority of cases). The notch cut is aimed in the direction you want the tree to go. I cut the upper part of the notch downward at an angle of about 70 degrees. The lower part of the notch cut angles upward at about 20 degrees, for a total of 90 degrees. This allows the tree to travel a full 90 degrees before the two sides of the notch meet each other and break the hinge. The depth of the notch need only be 1/5 to 1/4 the diameter of the tree. The felling cut is usually made slightly higher (about 1" for a 12" tree) than the intersection of the two notch cuts. This gives the hinge a little more flexibility. The felling cut is made parallel to the ground (assuming level ground), NOT down at some crazy angle like some people like to do for god knows what reason. The biggest key to the whole process is to leave an uncut strip of wood (the "hinge") between the notch and felling cuts, about 10 percent of the diameter of the tree. This controls the direction of fall, since the trees fibers are extremely resistant to tearing out sideways but will much more readily fold over. I use the example of the popsicle stick - no one I know can break one sideways, but you can snap one in half the flat way all day long.
If the tree has a slight lean in the direction you want it to go, great - just do the above and over she will go. If it is neutral or slightly backwards in lean, 1 to 3 plastic wedges bashed into the felling cut will usually force it over. I say 1 to 3 because if 1 doesn't do it, put 2 together and bash them in. If the tree is leaning heavily in the wrong direction, mechanical means must be used, as in a good stout rope and preferably a winch, but you can use whatever else you think is safe - tractor (pulling from the drawbar of course), motor vehicle, come-along, pulleys, whatever. Just make sure you have no doubts about what you are doing. If you're not sure, don't do it.
One more thing: trees with heavy leans have probably killed more people than anything else, except maybe for falling branches. This leads to a situation called "barber-chairing", where the tree splits up the middle long before the felling cut reaches the intended hinge. To avoid barber-chairing you must employ a plunge cut into the tree a hinge-width behind the notch cut, thereby establishing the hinge, and then proceeding with the felling cut toward the back side of the tree, away from the notch cut. When all of the holding wood has been severed, the tree is then free to fall in the direction of its natural lean, with the previously established hinge guiding its direction of fall in a controlled manner. Plunge cuts cannot be done with safety (anti-kickback) chain, and can be extremely dangerous. For these reasons, I recommend leaving trees with heavy leans to professionals, or very, very good non-professionals
Hope this helps, and again, if you have any doubts about what you are doing, please don't do it.
