If they're that close to the fence, which one are you going to take down in a few years, the trees or the fence? Those things grow about three feet or more per year, and can hit 60 feet tall.
As long as you don't break the roots up, you can stake the trees to straighten them. They're young and it's not likely you'll hurt them... they're very tough trees. It will take a year, two at the most, for them to straighten up and adjust their roots accordingly. By then, you should be able to remove the stakes. I usually use three T-posts and polyester webbing for this, but you can use rope if you have to. Be sure to cut some garden hose or similar and run the rope through pieces of it where it goes around the tree. You don't want it damaging or cutting into the bark.
If they're very close to the fence, you'll need to get your neighbor's permission to place stakes on that side of the trees, and run the webbing/rope through the fence, if necessary.
