Am I right in thinking that the trunk suddenly doubles in width part way up? That _is_ a strange feature! Where did you get these trees from; it could be the result of a graft. It's hard to tell from the picture - would you say the foliage coming from below the join is different from that above?

that is most peculiar. Hannah makes a good point, if it is a graft and they did not pick the same species of tree, then the uppermost may be quicker to grow than the rootstock, which in that case is a real stinker, you didn't raise these from seeds did you? I have a very wierd apple seedling which has never turned green yet, it has a white stem, and white leaves still and is just starting to open up its second set of true leaves, however, i think it was a genetic default and is not able to make chlorophyl, leading to is very very slow growth. Its about 2 weeks old and is still only 2 inches tall. takes full sun however.