If one broadens one's definition of aliens to include any alien life, even as tiny as a microbe, then the possibility of discovering it within our own solar system is still very real. One of the leading candidates is currently Mars, where water, one of the leading prerequisites of terrestrial life, has been found in its polar ice caps and soil.
I'm not 100% sure that there are other life forms in our solar systems, but I hope there are. If this were to be discovered it would an amazing feat in science and technology. We would be able to communicate with a totally new life form, and probably learn so many new things that could possibly advance man kind.
There is likely some form of alien life in the solar system. It may not be the kind of aliens portrayed in Hollywood movies, but there are probably some other forms of life beyond Earth. Scientists will likely discover new forms of life in the solar system in the future. When doing so, there will be a debate over how to classify these creatures.
No, I don't think aliens likely live in our solar system. It seems very likely that aliens exist somewhere in the universe, but planets in our solar system don't seem to be able to support life. Many people have put forth theories that aliens exist on our own planet. Who knows where they're located.