Agree with everything Davros has said. There us no thimerosil in MMR. one of the main pieces of evidence for a link between MMR and autism is that MMR dmamaged chilren seem to have vaccine strain measles in their guts and spinal fluid. However this is not proof of a link. There are various theories as to why giving MMR may be a problem rather than giving singly. Nothing very concrete though. Having chickenpox around the time of having MMR doesn't seem to do anyone any favours.
Mumps itself is not usually serious before the age of puberty (and then its not usually serious.) The main complication of mumps in children and this is rare still is meningitis- but this is aspetic (viral) meningitis- not the scary hideous meningococcal, or hib meningitis. Think its unpleasant but full recovery is normal (with no treatment).
Bascially all you have to decide it a)which diseases you want to immunise against and b) how scared you are of the MMR. Having a host of autoimmune conditions in your family may put you at higher risk.
The threads will always be cconfusing as there is no right or wrong answer. There are no definites in which ever course you choose to take. You just have to decide which one you can best live with.