Feline leukemia requires direct cat-to-cat contact to spread, it can't survive in the environment for very long. So the chances of bringing it home on your hands or clothes is slim to none. And keeping your cats' vaccines current makes the chances slim to none that they'd catch it even if they were to come in direct contact with an infected cat. This is EXACTLY why everyone should vaccinate ALL their animals. Your cats are very well-protected. You don't need to worry.
The feline leukemia vaccine does NOT cause feline leukemia in any way, shape or form. ALL cat vaccines carry a very small risk of causing tumors to form (vaccine induced sarcoma) but it's much less of a risk than leaving your animals unvaccinated. It's still unknown if it's something in the vaccines, or just the physical trauma from the injection that causes it. Dogs don't seem to make these tumors, just cats and horses. And most vets now give cat vaccines in the rear, because it's much easier to remove a tumor from a rear leg should one form. And since feline leukemia is ALWAYS fatal, it's much better to get the vaccine done.