Please read the article at the link below. It has a link at the top left to find a conservator in your area when you are done reading it. At the very least please consult with a conservator in your area before attempting any cleaning of the painting. You never know the painting may have a high value. If anything it can bring a bit of beauty and joy to you, and your friends and family, through the comming years if cared for properly.
Best regards; The Home Smithy
Ok here is a do it yourself site made by a professional conservator. It has all the information you need to do most any cleaning or repair of an oil painting.
Hmmm Now who would have thought that you can use an onion to clean an oil painting.
Very interesting reading.
As for the chemicals they are all availablre at most hardware and home improvement centers. Or in your home pantry it seems.